GlaxoSmithKline announced Wednesday that it has made a tender offer to acquire Human Genome Sciences for $13 per share.
The offer represents an 81 percent premium over HGS' closing share price on April 17, which was the last day of trading before HGS publicly disclosed GSK's private offer for the company.
GSK's original unsolicited offer to buy HGS for $2.59 billion was rejected.
HGS has since begun what it calls a strategic alternatives review process, which GSK said Wednesday it will not participate in.
GSK and Human Genome collaborated on the lupus drug Benlysta, and they've partnered on two experimental medicines for diabetes and preventing heart attacks that are in the late stages of clinical trials.
"The reason why we're interested in the deal with Human Genome is to simplify our relationship on Benlysta, to drive the performance of Benlysta for the benefit of our shareholders and to take efficiency opportunities that we believe exist, " GSK CEO Andrew Witty said last month.
GSK has about 3,800 workers at its North American headquarters in Research Triangle Park and 600 at its manufacturing plant in Zebulon.