Hippocampal neurones, from embryonic rats, were cultured for different times and the extension of dendrite-like processes was analysed morphologically and by immunofluorescence, using microtubule-associated protein 2 (MAP2) as a marker. Simultaneously, the changes in phosphorylation in MAP2 were analyzed and a correlation between dendrite sprouting and an increase in MAP2 phosphorylation was found. Phospho-MAP2 was cleaved by Staphylococcus aureus V8 protease limited proteolysis and its phosphopeptide pattern was compared to that obtained with two protein kinases (calcium/calmodulin-dependent kinase and protein kinase C) in vitro. An involvement of calcium/calmodulin-dependent protein kinase in the phosphorylation of MAP2, occurring simultaneously with dendrite extension during neuronal differentiation in vitro, is suggested.