Heterologous double-antibody radioimmunoassay methods are described for the measurement of circulating levels of rhesus monkey (Macaca mulatta) FSH and LH; the latter assay is also applicable to rhesus chorionic gonadotropin (CG) estimations. The FSH assay utilizes purified rat FSH for trace, either of two anti-human FSH antisera and a semipurified rhesus pituitary standard. The LH assay utilizes purified ovine LH for trace, an anti-human CG antiserum and the same rhesus pituitary standard. The use of these systems obviates the necessity of purifying rhesus gonadotropins which are required for the development of homologous radioimmunoassay systems.