Murine endothelial cell lines containing middle T antigen provide a good model to study the biology of capillary cells of different anatomical districts. These cell lines obtained from skin (sEnd.1), brain (bEnd.4), thymus (tEnd-1) and embryo tissue (eEnd.1) are activated by platelet-activating factor (PAF). PAF, but not lyso-PAF or the enantiomer (S)-PAF, induces the rapid translocation of protein kinase C (PKC) from the cytosol to the membrane. Maximal translocation of the enzyme is achieved after 5 min in all cell lines tested. The ED50 of PAF able to promote PKC translocation has a value of 5 nM in sEnd.1, bEnd.4 and eEnd.1, and 20 nM in tEnd.1, suggesting a different sensitivity between these cell lines. The data indicate that PAF activates capillary cells, thus explaining its activation of microvascular beds.