Differential development of reproductive characteristics and sex organs among age classes of male white-tailed deer (Odocoileus virginianus) during the breeding season was studied in west-central South Carolina. Blood samples and reproductive organs were obtained from 292 hunter-harvested deer from 26 October through 21 December 1985. Peak serum testosterone concentrations of ≥3.5-yearold deer occurred during the first week of the study, whereas peak concentrations in younger deer occurred approximately 4 weeks later. Testosterone concentrations were higher (P < 0.03) in older age classes. Data support the hypothesis that younger males reach peak rutting condition later than prime-aged (≥3.5 years old) individuals. Correlations (P < 0.01) among testosterone concentration, testicle length, and scrotal circumference were observed in yearling and 2.5-year-old bucks, but not in the ≥3.5 year olds.