BTP, which produces a range of specialty chemicals, including disinfectants, agrochemicals and brewing agents, jumped 24 pence to 523.5. It has risen 24 per cent during the past 10 trading days.
Sales of Viagra, which was introduced a month ago, are likely to top $1bn in the first 12 months, and may reach as much as $2bn in 1999, analysts have estimated.
"It's such a powerful story in terms of sentiment. You're going to get a lot of publicity for Viagra," said Jeremy Chantry, an analyst at Credit Lyonnais Securities.
Mr Chantry had a "buy" stance on the company even before news of Viagra's potential was released.
Mr Chantry said that sales related to the pill could account for about 3 per cent of BTP's profit in a couple of years.
Traders and investors said Credit Suisse First Boston analysts repeated their "buy" stance on the stock and set a price target of 615p.Reuse content