In situ hybridization of a 3H-labeled probe containing a fragment from PRP-1, a genomic clone with human salivary proline-rich protein gene sequences, revealed significant labeling on the short arm of human chromosome 12 in metaphase preparations from two individuals. Fifty-three percent of metaphases exhibited labeling on one or both chromosomes 12. Additional cells scored at the 850–1,000 band level revealed a significant proportion (52% [32/61] grains, p < 0.005) of the labeled sites on chromosome 12 to be on band 12pl3.2. This probe for a human salivary proline-rich protein gene fragment, probably PMS, is from a cluster of 13 linked genes designated as the human salivary protein complex (SPC). Studies of the DNA of human-mouse somatic-cell hybrids have assigned the SPC to chromosome 12, but have not provided a regional localization (Azen et al., 1985). This paper reports the localization of the SPC to a specific chromosomal band, 12pl3.