His suggestion that the drug group's shares could collapse to 320p sent the price tumbling 27p at one time. It closed 19p lower at 553p.
The Feinberg comments underlined the nervousness and volatility surrounding Glaxo. The US fund manager seems to have little, if any, following in the UK. 'I've never heard of him,' said one London drug analyst. Another asked: 'Larry who?'
Glaxo is, of course, a soft target. The Clinton administration's probe into US healthcare could lead to enforced cuts in drug prices, thereby putting margins under pressure. With the report of the healthcare 'task force', led by Hillary Clinton, at one time expected next month but now likely to materialise in July or August, drug shares are likely to remain under the weather.
But there appears to be a growing belief among drug houses that any Clinton recommendations may have a greater impact on services, rather than products.
Certainly the rumoured torrent of US selling of Glaxo has yet to materialise. As the price has slumped from a 943p high there has been little more than a steady stream of selling by American investors, who have, however, been scrambling out of their own drug stocks.
In the past six months the US shareholding, as represented by Bank of New York American depositary receipts, has fallen from 23.75 per cent to 22.95 per cent. The US stake peaked at 27.5 per cent a year ago.
Despite the weakness of Glaxo, the shares remain one of the market's outstanding performers. They were equal to 15p in 1980.
Other drug shares were mixed. Bespak dipped 20p to 658p following a profit warning by a US company with which it has trading links, and Medeva remained sensitive, down 2p to 199p.
The rest of the stock market started the final leg of the Easter account on a confident note, although trading was thin. Strength in Hong Kong (stemming from the renewed talks over the colony), New York and Tokyo helped sentiment. The French interest rate cut and further signs that the UK economy is pulling out of recession also helped.
The FT-SE 100 index closed 25 points higher at 2,846.8 and the second-string FT-SE 250 index also made headway. Cable and Wireless, the HSBC and Standard Chartered banking groups, and Inchcape were among the beneficiaries of Hong Kong's strength.
BAA, the airports group, rose 10p to 793p on the 6.2 per cent increase in March passenger traffic, and British Aerospace put on 5p to 278p on continuing speculation that the Indonesian order for Hawk aircraft is about to be signed.
Mirror Group Newspapers gained 6p to 127p on talk of a bid. MAI, the advertising and money- broking group which is the favourite to pounce, edged ahead 1p to 182p.
The guessing game about the likely MB Caradon bid target continued, with Tarmac again coming in for attention. The shares gained 4p to 137p. Redland, up 5p to 439p, is also in the frame.
Water shares, which have been rising to new heights, took a bath as some suddenly became aware that higher prices meant dividend yields were shrinking. Anglian fell 8p to 538p and Thames 6p to 550p.
In surprising contrast, yield considerations continued to power electricity shares higher with many advancing to new highs for the year.
Aberdeen Petroleum was actively traded as its hostile bidder Pittencrieff picked up nearly 2.5 million shares at 14.83p. Pittencrieff now has 26.6 per cent of AP.
Although trading was thin there was continued action among fringe shares. Kewill Systems, the computer group which has been strong since it sold its troublesome German operations, advanced a further 23p to 161p following a Kleinwort Benson presentation.
Honeysuckle, the fashion group, which recently announced encouraging results, added 8p to 60p, and Hoskins Brewery, where another shareholding rebellion is fermenting, frothed 6p higher to 53p. Richard Cattermole, who led last year's unsuccessful uprising, has sold his remaining 183,400 shares.
HTV, attracting buy recommendations, rose 6.75p to 46.75p.
The FT-SE 100 index closed 25 points higher at 2,846.8 and the FT-SE 250 index 17 up at 3,101.3. Turnover was a subdued 419.5 million shares with 28,120 bargains logged. The account ends on Friday with settlement on 26 April. Government stocks were firm.
The stockbroker Panmure Gordon believes Gibbs Mew, the Salisbury brewer which last year fought off a takeover bid from Brierley Investments, is staging a strong profits recovery. It expects pounds 1.1m (against pounds 633,000) for the year just ended with pounds 2.8m likely this year. Gibbs has absorbed the UK D wholesale drinks business since the bid battle. Its shares rose 9p to 204p, highest for two years.
RPC Group, a supplier of rigid plastic packaging, is coming to the stock market next month through a placing by Baring and Cazenove. The company was formed as a pounds 33.4m management buyout from Reed Packaging, a subsidiary of Svenska Cellulosa Aktiebolaget. RPC achieved an operating profit of pounds 5m in the year to March 1992, and is said to have made further progress in the year just ended.Reuse content