GlaxoSmithKline has further reduced its stake in the USA's Quest Diagnostics and netted $256 million in the process.

Over the last few days, GSK has sold over 1.2 million shares in Quest on the open market, bringing in $56.1 million. It also sold 4.5 million shares back to Quest for around $200 million.

The transactions mean that GSK now holds a 16.5% stake in the US firm, which has a market value of about $1.36 billion. The UK-based drug major said that the shares were sold "as part of a gradual reduction in the group's holding and to take advantage of Quest's recently expanded share repurchase programme".

GSK originally acquired the shares after selling its clinical laboratories business to Quest in 1999.

Meantime, Glaxo is being mentioned this morning as a potential purchaser for US skincare specialist Stiefel Laboratories. The Wall Street Journal reported that the privately-held company is believed to have put itself up for sale and such a trasaction could bring in $3-$4 billion.

Other companies mentioned as possible buyers include Johnson & Johnson and Novartis.