An improved method is described for the isolation of FSH from bovine pituitary glands. The purification procedure consisted of an initial ammonium sulphate precipitation step followed by triazine-dye chromatography, immobilized metal affinity chromatography, high-performance anion-exchange chromatography and gel filtration. Three highly purified bovine FSH preparations (designated bFSH-A, -B and -C) were obtained, giving yields of approximately 5.7 mg FSH/kg bovine pituitary glands (wet weight), with specific radioreceptor activities for bFSH-A, -B and -C of 61, 25 and 29 units (NIH-FSH-S1)/mg protein respectively. The corresponding biological activities were 217 (bFSH-A), 62 (bFSH-B) and 86 (bFSH-C) units/mg, as measured by an FSH in-vitro bioassay. LH levels were found to be < 1% (w/w) as determined by an LH in-vitro bioassay. SDS-PAGE of these bFSH preparations under reducing conditions in 16% polyacrylamide gels showed two major silver-staining bands of apparent molecular masses 19.5 kDa and 15.8 kDa. Their amino acid compositions were in close agreement with the expected composition, based on the bFSH cDNA sequence and results reported by other investigators. N-terminal sequencing of the bFSH-A preparation yielded two major sequences consistent with alpha- and beta-subunits, and a third minor (< 20%) sequence consistent with the alpha-subunit clipped at amino acid residue 6. It was concluded that the bFSH purification procedure reported here is a rapid method which produces bFSH in high yield and high purity, with radioreceptor and in-vitro specific activities comparable with those previously reported by other investigators.