Chromosome assignment of the rat histone genes Hit, Hld(H1.4), Hlfv, (H1(0)), Th2a and Th2b is described. The testicularly expressed histone genes Hit, Th2a and Th2b could be assigned to rat chromosome (RNO) 17 by PCR analysis of somatic cell hybrid DNAs. The Hid gene was mapped to RNO 17p12 --> p11 by FISH. These genes might form a histone gene cluster homologous to that found on HSA6p21.3 in humans and MMU13A2-3 in mice. The rat histone Hlfv gene was assigned to RNO7 by PCR. This result allows the inclusion of rat Hlfv to an established conserved group of syntenic genes in rat, mouse and human on chromosomes RNO7, MMU15 and HSA22, respectively.