Danaher (NYSE:DHR) and Blackstone Group, 1 of the world’s largest private equity players, have joined forces to pursue a buyout of Johnson & Johnson‘s (NYSE:JNJ) Ortho Clinical Diagnostics unit, according to Reuters.

Johnson & Johnson is seeking a 2nd round of bids for the OCD blood testing division, the new service reported, citing "people familiar with the matter."

J&J tapped JPMorgan Chase & Co. to shop the business in September, receiving bids from some of the biggest names in private equity by the end of that month, including Blackstone Group, Kohlberg Kravis Roberts, Bain Capital, Carlyle Group and BC Partners.

Now, the sources say, the DHR/Blackstone group is vying with Bain, Carlyle, BC Partners and a joint bid from CVC Capital Partners and Leonard Green & Partners. The OCD business is now said to be able to fetch as much as $4 billion, down from earlier estimates of $5 billion, according to Reuters.

Danaher and Blackstone got familiar 2 years ago in the battle over another diagnostics property, Beckman Coulter, which Danaher wound up acquiring for $6.8 billion in 2011.