The drugs troglitazone and metformin are used to reduce the degree of insulin resistance in type 2 diabetes. Both compounds act through different mechanisms which might include opposing effects on the production of adiponectin, an insulin-sensitizer released by adipocytes. This study compared the effects of troglitazone and metformin on adiponectin production by 3T3-L1 adipocytes during 48 h culture. Troglitazone increased adiponectin mRNA and protein expression as well as release, whereas metformin did not affect transcription but reduced protein expression and release. The effect of metformin was also seen with phenformin, and with low-glucose culture, all conditions with a reduced mitochondrial activity and an activated AMP activated protein kinase (AMPK). Addition of the AMPK activator 5-aminoimidazole-4-carboxamide-riboside (AICAR) also caused a decrease in adiponectin protein expression. These data indicate that metformin and troglitazone exert opposing effects on adiponectin expression and release by differentiated 3T3-L1 adipocytes. The metformin-induced suppression involves an activation of AMP activated protein kinase.