Activin is a multifunctional hormone playing a major role in the regulation of reproduction and growth and development. We performed a genomewide scan using multipoint linkage analysis implemented in a general pedigree-based variance component approach to identify genes with measurable effects on variation in the activin-to-estrogen ratio in baboons. A microsatellite polymorphism, D19S714, which maps to human chromosome 19p13.2, showed marginal evidence of linkage with a lod (log10 of the odds in favor of genetic linkage) score of 1.95 (0.014). This region contains several potential candidate genes including PKA (protein kinase, cAMP-dependent, catalytic alpha) and the gene pair JUN-B and JUN-D. This is the first evidence of a quantitative trait locus with a significant effect on the activin-to-estrogen ratio.