Bioactivity-directed fractionation, using brine shrimp lethality and murine hypoglycemia, of an ethanol extract prepared from Tillandsia usneoides, led to the isolation of four apparently bioactive compounds from the water-soluble fraction. The compounds were identified as citric acid, succinic acid, 3-hydroxy-3-methylglutaric acid (HMG), and 3,6,3',5'-tetramethoxy-5,7,4'-trihydroxyflavone-7-O-beta-D-g lucoside. The brine shrimp lethality of the acids was simply due to acidity; however, HMG elicited significant hypoglycemic responses in fasting normal mice. Ethyl and methyl esters of citric acid were prepared and tested in the murine hypoglycemic assay. Five of the predominant sugars were identified by tlc. Free thymidine was also isolated. Further evaluation of HMG and other potential inhibitors of HMG CoA lyase, in the treatment of symptoms of diabetes mellitus, is suggested.