In crude extracts of Candida maltosa, about 12 proteins are phosphorylated in the presence of cAMP or of a catalytic subunit of cAMP-dependent protein kinase. A strongly labelled protein spot occurred in the position of fructose-1,6-bisphosphatase both after electrophoresis of crude extracts incubated with cAMP and of a partially purified fructose-1,6-bisphosphatase incubated with a catalytic subunit of cAMP-dependent protein kinase. No phosphorylation of the cytoplasmic malate dehydrogenase could be detected. From these results it was concluded that cAMP-dependent phosphorylation plays an important role in the catabolite inactivation of fructose-1,6-bisphosphatase in Candida maltosa, as described for Saccharomyces cerevisiae.