Blood samples were taken once per week for 4-7 weeks from 59 buffalo calves in 14 age groups, 1-2 months apart. Hormones were quantified by validated radioimmunoassays. Values of androstenedione and testosterone were low at birth (141.3 +/- 33.5 pg/ml and 18.0 +/- 2.9 pg/ml, respectively; mean +/- s.d.). Serum androstenedione concentrations gradually increased from birth until 8 months of age and declined (P less than 0.05) thereafter, whereas mean testosterone values were low up to 8 months and then significantly (P less than 0.05) increased as age advanced. LH concentrations averaged 2.12 +/- 0.47 ng/ml at birth. Thereafter, a decline in LH values was followed by an increase between 6 and 15 months of age. We conclude that, in buffalo bull calves, the pubertal period occurs from about 8 to 15 months of age. For pubertal buffalo bulls 15-17 months of age, serum concentrations of androstenedione, testosterone and LH were 156.9 +/- 54.6 pg/ml, 208.4 +/- 93.8 pg/ml and 2.10 +/- 0.70 ng/ml, respectively.