Warnings that it could take a decade to fill the gap left by Pfizer, which is closing its site in Sandwich, have come from the leader of Kent County Council.
The drugs giant said in February that its east Kent base, which employs 2,400 people would close, but it would keep about 350 jobs at the site.
Councillor Paul Carter said there had been interest in the site, but it could take 10 years for Kent to recover.
He said a purchaser would need patience to allow time for the site to deliver.
Mr Carter said creating 2,500 to 3,000 jobs in pharmaceutical research was "a big ask in a completely changing world".
He said: "I'm fully aware of that and, if we can build up in 18 months to two years' time and have a thousand good quality jobs on that site, I think we've started to deliver the success."
Enterprize zone bid
He added: "It's going to take five or 10 years to grow that, but time we need, and we need to make sure that hopefully we get a freehold purchaser that they've got the patience to allow that time to deliver."
John Westwood, real estate director at Pfizer, said there had been interest in the site.
"There aren't a huge number of organisations or individuals with appetite for it but nevertheless there has been interest, and we are continuing to pursue those avenues," he said.
After the closure was announced, a task force of politicians was set up to support new business and employment on the Pfizer site.
This summer, plans were put forward to turn the research and development facility into an enterprise zone.
Pfizer said there will be a phased exit of the the site in Ramsgate Road by 2012. The site was put on the market in June.
In June, the company said it would retain some operations at the facility, preserving about 350 jobs.