The seven Y-chromosomal STRs DYS 19, DYS385 I/II, DYS389 I/II, DYS390, DYS391, DYS392 and DYS393 were amplified using two multiplex PCRs. The optimization of the PCR conditions led to reliable and sensitive systems. Co-amplification of the amelogenin locus was possible in both multiplex systems. In a population sample of 151 Bavarian males, a gene diversity of 0.99 was observed. Sensitivity studies revealed a detection limit of 50 pg DNA per 25 microl reaction volume. PCR experiments with combinations of male/male and male/female DNA showed that in male/male mixtures, the minor component could be detected up to a ratio of 1:15, whereas in male/female mixtures the male component could be found in a higher ratio up to 1:60.