The experiment involved 3 successive phases in rearing Holstein heifers at Corozal on pastures of mixed grasses, fertilized annually with 168, 56 and 112 kg/ha of N, P2O5 and K20, respectively, in 3 applications. Mean initial age was 9 months and liveweight (LW) 167 kg. In phase 1 (91 days), 39 control animals stocked at 5/ha and not supplemented gained 0.41 kg daily, inferior (P < 0.01) to the gain of a like number supplemented with 2 kg daily of 14% crude protein concentrate (0.64 kg), 8.6 kg of concentrate per kg of extra gain over the control. In phase 2 (182 days), 32 animals stocked at 4/ha gained less (P = 0.01) per head than 24 stocked at 3/ha (0.53 vs. 0.59 kg daily), but total gain per ha was 16.4% greater for the former. During 259 days of phase 3, while 3 groups of 19 each remained intact, grazing at 3.75 animals/ha without supplementation (treatment 1) resulted in lower (P = 0.01) gain than treatments 2 and 3, involving concentrate supplementation at 2.5 or 4 kg daily beginning 200 or 125 days before expected parturition (0.57 vs. 0.64 and 0.62 kg, respectively), but supplementation increased gains over the control very inefficiently. Mean LW increased from 318 kg in all 3 groups to 485, 513 and 497 kg in treatments 1, 2 and 3, respectively. Only heifers of the latter 2 groups continued to receive concentrates after returning to their home farms in Cayey and Manatí until first calving. All animals received usual herd management postpartum. Mean 305-day first lactation milk production was 4292 kg in 18 control animals of phase 3, surpassing (not significantly, P = 0.05) productions of 3,771 and 3,869 kg by 16 and 17 former treatment 2 and treatment 3 animals, respectively. Stocking rates employed at each stage seemed suited to available pastures, and concentrate supplementation was unnecessary for rearing dairy heifers under these conditions.