GTP, GTP-gamma-S and Gpp(NH)p produced a significant activation of Mg2(+)-dependent adenylyl cyclase in permeabilized cells of Candida albicans. This activation was inhibited by GDP-beta-S. Maximal stimulation (4-6 fold) was obtained when Mg2+ and GTP-gamma-S were added during permeabilization. The guanine nucleotide-stimulated activity could be further activated by glucagon in a dose dependent manner being the maximal stimulation (4-5 fold) attained at 10(-6) M glucagon. Addition of the hormone to yeast cells incubated under conditions conducive to produce germ tubes blocked hyphal development and promoted multibudded cell morphology.