The aim of this study was to evaluate in premenopausal women (six endurance-trained nonobese, six sedentary nonobese, and five sedentary obese) the suppression of whole body and regional lipolysis by insulin. Lipolysis was determined using 2H5-glycerol infusion and microdialysis of sc adipose tissue (AT) during a two-stage [6-10 (low; LO) and 12-20 (moderate; MOD) mU/m x min] hyperinsulinemic-euglycemic clamp. Microdialysis probes were positioned in abdominal and femoral sc AT to monitor interstitial glycerol and nutritive blood flow. Basal plasma glycerol was 102 +/- 9, 52 +/- 6, and 143 +/- 30 micromol/L in endurance-trained nonobese, sedentary nonobese, and sedentary obese, respectively (P < 0.05, sedentary nonobese < endurance-trained nonobese, sedentary obese). The plasma glycerol concentration was decreased (P < 0.05) to a greater extent in endurance-trained nonobese and sedentary nonobese [both to approximately 50% (LO) and approximately 45% (MOD) of basal] than in sedentary obese [to 72% (LO) and 63% (MOD) of basal]. The rate of appearance of glycerol was suppressed to 36 +/- 7%, 44 +/- 10%, and 62 +/- 7% of basal during LO in endurance-trained nonobese, sedentary nonobese, and sedentary obese, respectively (P < 0.05, endurance-trained nonobese < sedentary obese), and to 34 +/- 3%, 36 +/- 5%, and 53 +/- 8% of basal during MOD, respectively (P < 0.05, endurance-trained nonobese < sedentary obese). There were no between-group differences in the suppression of lipolysis in abdominal sc AT, as evidenced by similar reductions in dialysate glycerol levels [all to approximately 65% (LO) and approximately 55% (MOD) of basal]. Femoral dialysate glycerol was reduced (P < 0.05) more in sedentary nonobese and endurance-trained nonobese (to approximately 75% of basal) than in sedentary obese (to 90% of basal) during LO, but to a similar extent (to approximately 60% of basal) in all groups during MOD. The results indicate that the sedentary obese women had whole body resistance to the suppression of lipolysis by insulin. Intraabdominal AT may be the site of resistance, as resistance was not evident in abdominal or femoral sc AT.