Recent evidence has suggested that extensive changes in the phosphorylation profile of red cell membrane proteins are associated with the invasion and development of the malarial parasite. In order to further define the role of parasite protein phosphorylation in these events we have looked at this phosphorylation using: (1) continuous metabolic labelling with [32P]orthophosphate, (2) pulse-labelling with [32P]orthophosphate and [35S]methionine, (3) autophosphorylation of infected cells using [gamma-32P]ATP, (4) invasion of prelabelled red cells. Many parasite proteins were labelled, some differentially according to the phosphorylation protocol employed, and we were able to partially characterise several of the major parasite phosphoproteins in terms of their association with host cell membrane and the stage specificity of phosphorylation.