Protein kinase activity was demonstrated on intact Leishmania aethiopicarnpromastigotes but not on heat generated "amastigotes". Similar work conducted on lysedrncells revealed enzyme activity in soluble and particulate fraction of flagellated parasites.rnEnzyme on intact cell plasma membrane preferred Histone V-S over protamine asrnin vitro substrate whereas enzyme from soluble or particulate fraction of lysed cellsrndisplayed the reverse in vitro preference. On the other hand enzymes from both intact andrnlysed cells were inhibited by Staurosporine and Formycin ATP.rnIncubation of intact stationary phase parasites with t 2pJ ATP led tornphosphorylation of eight protein bands. Similar experiment conducted using lysed cellsrnrevealed twenty bands. Incubation of the cells with [32pJ with the assumption of generatingrnintracellular t2 P ] ATP also led to a patte111 of phosphorylation similar to that of lysedrncells. It follows from the above that Leishmania aethiopica promastigotes possess bothrnextra and intracellular endogenous substrates of protein kinases.rnMeasurement of soluble kinase activity revealed increased activity as cells wentrnfrom log to stationary phase where intact cell activity remained constant. Exposure tornelevated temperature (37') induced transformation of the promastigotes to aff/agellatedrnorganism "amastigotes". This transformation resulted in a potent down regulation of bothrnthe soluble 'and the ecto kinase activities.rnIn the promastigotes, Staurosporine caused morphological alterations. On the otherrnhand Formycin ATP had a profound inhibitDlY effect on thymidine incorporation andrncellular proliferation. These effects of Formycin ATP do not seem to be wholly accountedrnby its protein kinase inhibitory activity.rnA classical protein kinase C like activity could not be detected in the promastigotes.rnHowever, evidence for the probable presence of a phorbol ester insensitive, calcium andrnphospholipid independent protein kinase C is presented. All the same these observationsrndo not rule out the presence of more than one subclass of protein kinases.rnThis work suggests that major protein kinase activities may be involved in thernregulation of proliferation, development and adaptation to "hostile" environment ofrnLeishmania aethiopica promastigotes. It also argues that the continued study of key eventsrnin the biology of this organism is cTilcial in the development of better therapeuticstrategies.