Aqueous extracts of Croton cajucara bark are used in folk medicine to treat hepatic and gastrointestinal disorders and as a coadjuvant in weight-loss programs. We examined the effect of treating rats for 15 days with a 5% aqueous extract of C. cajucara on body weight and food intake. The epididymal adipose pads were removed and the lipolytic responses of isolated adipocytes to isoprenaline, noradrenaline (norepinephrine), BRL37344 and adrenaline (epinephrine) were analysed in the absence or presence of metoprolol or ICI118,551. Treated rats had a significantly lower weight gain than control rats, with no difference in food and liquid intake, epididymal fat-pad weight or basal glycerol release. The sensitivity of the lipolytic response to isoprenaline and adrenaline was significantly higher in adipocytes from treated rats. The sensitivity to noradrenaline or BRL37344 was unaltered. Metoprolol shifted the dose-response curves to noradrenaline to the right in adipocytes from control and treated rats; the dose-response curve to isoprenaline in adipocytes from control rats was also shifted to the right. In adipocytes from treated rats, the dose-response curve to isoprenaline was unaltered by metoprolol but was shifted to the right by ICI118,551, a beta(2)-adrenoceptor antagonist. We conclude that in adipocytes from treated rats there is an increase in the lipolytic response to non-selective agonists (isoprenaline and adrenaline) mediated by beta(2)-adrenoceptors, with no alteration in the responses mediated by beta(1)-adrenoceptors (noradrenaline) or beta(3)-adrenoceptors (BRL37344). This effect could increase the role of adrenaline as an endogenous stimulator of lipolysis.