Earlier reports seemed to indicate that the cytoplasmic intermediate filament protein vimentin and the nuclear intermediate-type filament proteins A and C lamins are expressed in a coordinate manner in human myeloid cells. We have comparatively studied the expression of the vimentin and the A/C lamin genes at the RNA and protein levels in human U-937 promonocytic and HL-60 promyelocytic cells treated with differentiation inducers. 12-O-Tetradecanoyl phorbol-13-acetate and cytosine arabinoside produced a coordinate and stable stimulation of both vimentin and A/C lamin expression in U-937 cells. A stable increase in vimentin expression was also produced by sodium butyrate and by dibutyryl cyclic AMP in U-937 cells and by dimethyl sulfoxide in HL-60 cells. In contrast, these agents produced only a transient increase in A/C lamin expression (maximum mRNA levels at 6-24 h), which later returned to expression levels similar to or even lower than those in untreated cells. Retinoic acid greatly inhibited vimentin expression in HL-60 cells, but it had little effect on A/C lamin expression. Taken together, the present results suggest that there are important differences in the mechanisms which regulate the expression of the vimentin and nuclear lamin genes, as well as in their implication in the differentiation of human myeloid cells.