Using monoclonal antibodies, we have studied the expression of lamins A,B,C and vimentin in mouse and human erythroleukemia cells. We have found that in contrast with previous reports these cells have all three lamins. Mouse cells lack vimentin, whereas human cells express it. Lamins B and C are the most abundant lamins, whereas considerably less lamin A is detectable. Our results argue that some mouse and human hemopoietic cells can express all three lamins and that production of vimentin does not necessarily precede that of lamins A/C, as other reports have suggested in the past. The data also show that the absence of a salt resistant inner nuclear matrix is not always related with the lack of lamins A/C and vimentin, as recently proposed.