The present study was performed in 17 nondiabetic subjects and was initiated to determine whether enhanced adipose tissue lipolysis, either basal or catecholamine induced (isoproterenol), and/or resistance to insulin inhibition of isoproterenol-stimulated lipolysis were correlated with resistance to insulin-mediated glucose disposal by muscle. Insulin-mediated glucose disposal was assessed by determining the steady state plasma glucose (SSPG) concentration during the insulin suppression test [180 min infusion of somatostatin (350 micrograms/h), insulin (25 mU/m2min), and glucose (240 mg/m2.min)]. On another occasion, plasma FFA and glycerol concentrations were determined at the end of 3 sequential infusion periods (IP): IP1, somatostatin (350 micrograms/h) plus basal insulin replacement (5 mU/m2.min); IP2, somatostatin (350 micrograms/h), insulin (5 mU/m2.min), and isoproterenol (270 ng/m2.min); and IP3, somatostatin (350 micrograms/h), isoproterenol (270 ng/m2.min), and insulin (10 mU/m2.min). SSPG concentrations correlated with FFA concentrations during all 3 infusion periods after adjustment for age, gender, body mass index, insulin concentration, and ratio of waist to hip girth (IP1:r = 0.61; P < 0.03; IP2: r = 0.70; P < 0.01; IP3: r = 0.65; P < 0.02). Correlations between SSPG and glycerol concentrations were also highly statistically significant (IP1: r = 0.62; P < 0.03; IP2: r = 0.65; P < 0.02; IP3: r = 0.70; P < 0.01). These results demonstrate for the first time that plasma FFA and glycerol concentrations are increased commensurate with the degree of resistance to insulin-mediated glucose disposal at a basal insulin level, in response to isoproterenol stimulation, and after insulin inhibition of isoproterenol-stimulated lipolysis.