Fifty crossbred cows (38 multiparous and 12 nulliparous) were used to evaluate in utero androgenization of heifer calves with trenbolone acetate. Three 200-mg trenbolone acetate (Finaplix-H) implants were implanted in the ear of treated cows (n = 24) on d 214 +/- 11 of gestation; the remaining animals (n = 26) were used as controls. Cows' rate of gain, serum levels of trenbolone acetate, gestation length, degree of dystocia, percentage bred back, days until conception, and 24-h milk production were evaluated. Fourteen-day weigh periods until parturition indicated that trenbolone acetate-treated dams had an increased (P < .05) average daily gain (1.05 +/- .1 kg) compared with control cows (.55 +/- .1 kg). Serum concentrations of trenbolone acetate were higher (P < .01) in treated cows with a peak at 9 d after implantation and returned to basal concentrations by d 77. Treatment did not affect degree of dystocia among all cows (P > .05) but seemed to increase (P < .01) the incidence of dystocia in nulliparous cows compared with nulliparous control cows. Gestation length and subsequent fertility were not affected by treatment (P > .05). Similarly, there was no difference in 24-h milk production (P > .05) between treated and control cows. Calf birth weight, phenotypic measurements at birth, vigor, average daily gain, carcass characteristics, and heifer reproductive tract and ovarian weights did not differ with treatment (P > .05). These data showed that late-gestation treatment with 600 mg of trenbolone acetate significantly increased weight gain of dams without demonstrating any androgenizing effects on the growth or physical characteristics of heifer calves.