I correlated the plasma titers of testosterone (T), estradiol (E), luteinizing hormone (LH), progesterone (P), corticosterone (B) and prolactin (Prl) with the reproductive behavior of breeders and adult and juvenal-plumaged helpers of the Harris' Hawk. During nest building, breeding males and adult male helpers had higher T levels than those in immature male helpers. Among females, only breeders had elevated T levels during nest building. During nest building, breeding females had higher E levels than those in adult and immature females helpers. Patterns of LH were similar to those of T and E. Concentrations of P and B varied only with handling time. During incubation, Prl titers were elevated only in breeding males and females. In contrast to other altricial species, all breeders showed no elevation in Prl levels during feeding of young. Among males, adult male helpers had the highest Prl levels while feeding young.