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 response of human adipose tissue was studiedin vitrowith or without halothane, the phosphodiesterase inhibitor theophylline, the lipase activator dibutyryl cAMP (dbcAMP), the α-receptor antagonist phentolamine, the nonselective β-receptor antagonist propranolol, and the selective β1-receptor antagonist practolol. In the absence of β-receptor antagonists low concentrations of halothane stimulated lipolysis. This effect was bhmted by β-receptor antagonists, indicating that halothane at low tissue concentrations may directly stimulate the β-receptors. The inhibitory effect of higher tissue concentrations of halothane was not the result of increased α-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.