The purification of rabbit lutropin is described. A product with a potency of 1.53 × NIH‐LH‐Sl was obtained as assayed by the ovarian ascorbic acid depletion assay. In a homologous radioimmunoassay, which is described, rabbit lutropin has a potency 4.83 × NIH‐LH‐Sl. In a radioligand assay, utilizing labeled ovine lutropin as the trace, the relative potency was 0.47 × NIH‐LH‐Sl measured by 50% inhibition comparison since rabbit lutropin response in this system did not parallel ovine lutropin.A counter‐current distribution procedure for separation of rabbit lutropin subunits is described. Amino acid composition of the isolated subunits and intact rabbit lutropin was determined. The carbohydrate composition of the latter is presented; only amino sugar determinations are available for the subunits. The NH2‐terminal amino acids are phenylalanine (alpha subunit) and alanine (beta subunit). Preliminary data on COOH‐terminal amin