The shares, in often busy trading, lost 18p to 663p, with NatWest Securities talking about the end of the Zeneca honeymoon.
The Zeneca split was, in effect, finally achieved on Tuesday when the drug group's pounds 1.3bn cash call was completed with an 85 per cent take-up.
During the float ICI managed comfortably to outperform its offspring with many taking the view it was better to stick with the rump of the business rather than be enticed by the attractions of the newly freed drugs side.
But the story has changed as Zeneca celebrated its freedom with modest progress and ICI fell 38p.
Today Sir Denys Henderson, ICI chairman, is due to address shareholders at their annual meeting. He is expected to strike an exceedingly cautious note.
NatWest believes shares of the shrunken group are a sell. 'Confidence in the US recovery has largely evaporated; Continental Europe is a disaster, the UK domestic recovery is muted,' it says.
This year profits are forecast at pounds 230m with pounds 380m likely next year. NatWest talks about pounds 1bn in 1997 but suggests any possible upside is fully reflected by the shares.
NatWest was not the only investment house to adopt a more bearish approach. Kleinwort Benson said 'sell' and the US group PaineWebber, which has been bullish on ICI, sharply reduced its profit forecasts. SG Warburg, behind the Zeneca float, denied stock market stories that it had downgraded.
The rest of the market had a lacklustre time, with the FT-SE 100 index falling six points to 2,894.7 in moderate trading. Drug shares were again disturbed by US influences; US selling of oil shares was another bearish factor, pushing, for example, British Petroleum down 7p to 304.5p.
Besides US apathy Glaxo Holdings had to contend with James Capel taking the knife to its profit forecasts. The stockbroker is thought to have cut current year's expectations from pounds 1.92bn to pounds 1.88bn. For the year ended in June about pounds 1.65bn is expected. Glaxo fell 6p to 573p.
Kingfisher, strong on Wednesday as Hoare Govett suggested its French operations could be performing ahead of expectations, was hit by Societe Generale Strauss Turnbull advising a switch into Boots, up 7.5p to 444.5p. Kingfisher lost 9p to 604p.
Smith New Court, the securities group, jumped 35p to 285p on the much better-than-expected profits and cash call. The stockbroker BWD Securities, with figures soon, advanced 11p to 96p in sympathy.
TI Group edged forward 4p to 340p on its French link-up and the paper group Arjo Wiggins Appleton fell 6p to 184p as the house broker, UBS Securities, downgraded.
Holiday shares were ruffled by the Whitehall inquiry into the packaged holiday industry. Airtours fell 15p to 324p. Interim figures, due on Monday, are expected to be accompanied by details of the acquisition of the family-owned Aspro holidays group. Airtours, which this month paid pounds 25m for the Hogg Robinson travel shops, tried unsuccessfully to take over Owners Abroad earlier this year. Owners fell 4p to 97p.
British Land slipped 4p to 319p. Its cash call attracted a 95.96 per cent take-up. SG Warburg placed the rump at 318p.
Lucas Industries' well-signalled analysts' meeting - the second this month - left the shares unchanged at 136.5p as the rumoured profit and dividend warnings failed to materialise.
British Aerospace was lowered 9p to 399p as worries surfaced about Taiwan's ability to raise the cash for the joint venture for short-haul jets. The pipe layer AH Ball tumbled 22p to 53p following halved profits.
Among smaller oil groups Aminex rose 3p to 30.5p in response to its plans to develop in the former Soviet Union and Pict Petroleum rose 7p to 122p following a North Sea gas find.
Anagen, a medical instrument group, demonstrated that not all new issues are wildly received. The shares, placed at 100p, quickly rose to 107p. But by the close they had relapsed to 91p.
British Dredging held at 115p as Redbird Holdings, a Panamanian company, said it had acquired 185,000 shares, lifting its stake to 5.06 per cent.
The department store group James Beattie shaded 1p to 143p. The stockbroker Harris Allday Lea & Brooks expects interim profits to be down by one-third to pounds 1.2m and has cut its year's forecast to pounds 6.3m. Last year's figure was pounds 6.83m.
In quiet trading the FT-SE 100 index fell six points to 2,894.7 and the FT-SE 250 edged forward 0.2 to 3,215.7. Turnover was 517.2 million with 25,354 bargains. The account ends on 2 July with settlement on 12 July. Lower interest rate hopes lifted government stocks.
Harmony, a loss-making pubs chain being reshaped into a property group, has a fascinating new shareholder - Multitrust, an ambitious group headed by Andrew Perloff. It has built a 4.39 per cent stake. In the past Mr Perloff has made his presence felt at Etonbrook Properties and Children's Medial (now Crabtree Holdings). Harmony shares edged forward 0.25p to 7p.
Shares of Rothmans International and Dunhill Holdings, surprisingly suspended on Wednesday, are likely to be requoted soon - possibly today. It was suggested that full details of the complex luxury goods and tobacco split have been completed and were ready to be released. In a few minutes of frantic trading as the market closed on Tuesday Rothmans surged 55p to 720p and Dunhill 62p to 405p.
Desmond Bloom, former guitarist for Screaming Lord Sutch, has started transforming Vizcaya Holdings, owner of a mothballed zinc mine in Spain, into a property group. Vizcaya is paying pounds 3.47m for properties with a yearly rental income of pounds 3.8m. The deal includes placings and a rights issue. The shares were suspended in April. Mr Bloom, formerly head of Dwyer, took over in December.