Karloo Kix, a stablemate of top pacer Karloo Mick, has become the second horse in a week to return a positive test to the banned substance boldenone.

Harness Racing NSW confirmed on Wednesday that the Barry Lew-trained Karloo Kix returned the positive test following his win at Newcastle on December 9.

The announcement came two days after the Luke McCarthy-trained Mach Wiper was found to have returned a positive test to boldenone, an anabolic steroid, after winning the Newcastle Cup on the same program.

Dates for the respective inquiries have yet to be determined.