Halothane has dual effects on lipolysis of human adipose tissue: at low tissue concentrations a stimulatory effect is found, while at higher tissue concentrations lipolysis is inhibited. The lipolytic resonse of human adipose tissue was studied in vitro with or without halothane, the phosphodiesterase inhibitor theophylline, the lipase activator dibutyryl cAMP(dbcAMP), the alpha-receptor antagonist phentolamine, the nonselective beta-receptor antagonist propranolol, and the selective beta1-receptor antagonist practolol. In the absence of beta-receptor antagonists low concentrations of halothane stimulated lipolysis, This effect was blunted by beta-receptor antagonists, indicating that halothane at low tissue concentrations may directly stimulate the beta-receptors. The inhibitory effect of higher tissue concentrations of halothane was not the result of increased alpha-receptor activity since addition of phentolamine did not inhibit this effect. High concentrations of theophylline or dbcAMP increased lipolysis in specimens exposed to halothane, but the lipolytic rate was still less than that found in specimens not exposed to halothane. The data thus indicate that the inhibitory effect of halothane is exerted at a step beyond the formation and degradation of cAMP.