Lesions of the medial preoptic-anterior hypothalamic (MP-AH) continuum made in juvenile male dogs (10–11 weeks of age) were previously reported to reduce juvenile mounting and virtually eliminate male copulatory behavior in adulthood. The effects of these lesions on the developmental patterns of serum testosterone (T) and luteinizing hormone (LH) were examined in the present study. Subjects with MP-AH lesions (MP-AH subjects) had a pubertal rise in serum T almost 2 months before subjects with sham lesions (SHAM subjects). Subsequently mean serum T of MP-AH subjects rose to levels significantly higher than those of SHAM subjects before falling back to the normal 3–4 ng/ml range of SHAM subjects at 10 months. There was no apparent relationship between secretion of LH and the acceleration and enhancement of serum T. These observations indicate that there can be impairment of male sexual behavior with lesions that accelerate and enhance sexual functioning in other respe