A combination of RT-PCR with cDNA library screening led to the identification of the human homologue of murine KIF4 (mKIF4), a microtubule-based motor protein. The nucleotide sequence of human KIF4 (hKIF4) comprised part of the 5' untranslated region (UTR), a long open reading frame (ORF) encoding 1232 amino acids, and the entire 3' UTR. Homologies with mKIF4 were 82% and 85% for nucleotides and amino acids, respectively. A single transcript of 5. 0 kb was highly expressed in hematopoietic tissues including fetal liver, spleen, and thymus, and adult thymus and bone marrow. Comparison of the ORF with that of mKIF4 revealed some dissimilarities in the putative cargo binding domain which might affect binding specificities.