Two related butenolides have been isolated from a culture broth of a strain of the fungus, Acremonium sp. Although the lactone acid (3) is a known compound, the structure of the lactone diacid (4), deduced by spectroscopic analysis, is assigned for the first time. This compound appears to be identical to a partly characterised metabolite isolated, along with 3, from Chaetomium indicum in 1953.