This study was undertaken to investigate temporal association between dexamethasone administration, OB gene expression, and leptin response in humans in the presence and absence of exogenous hyperinsulinemia. Six healthy males (age 24.5 +/- 1.0 yr, body mass index 26.4 +/- 1.0, body fat 16.2 +/- 1.8%) received 10 mg oral dexamethasone in five divided doses twice (protocols A and B) 1-2 weeks apart beginning at 0800 h on day 1 and ending at 0700 h on day 2. The dexamethasone administration was combined with two subcutaneous abdominal fat biopsies performed at 0800 h before and after dexamethasone administration (protocol A), or 4-h isoglycemic hyperinsulinemic (300 mU/m2 BSA/min, protocol B) clamp carried out between 0900 and 1300 h on day 2. OB gene expression (protocol A) did not change. In both protocols on day 2, the 0800 h leptin levels nearly doubled (P < 0.001), whereas 1300 h levels nearly quadrupled (P < 0.001). The elevation in leptin persisted until 0800 h of day 3 (24 h after last dexamethasone dose) with its subsequent rapid normalization. The short-term isoglycemic hyperinsulinemia (protocol B) had no additional effect on the postdexamethasone leptin response. We summarize that: 1) 24-h administration of dexamethasone has a marked stimulatory effect on circulating leptin levels but not on OB gene expression in the subcutaneous abdominal fat. 2) The effect is sustained for the next 24 h. 3) Short-term hyperinsulinemia has no additional effect. We conclude that dexamethasone is a powerful stimulator of leptin production in vivo through a mechanism that appears to be independent of OB gene transcription in the human subcutaneous abdominal fat.