The objectives of this study were to determine whether the addition of growth hormone (GH) to maturation medium and GH or insulin-like growth factor-I (IGF-I) to culture medium affects development of cultured bovine embryos. We matured groups of 10 cumulus–oocyte complexes (COCs) in serum-free TCM-199 medium containing FSH and estradiol with or without 100 ng/ml GH. After fertilization, we transferred groups of 10 putative zygotes to 25 μl drops of a modified KSOM medium containing the following treatments: non-specific IgG (a control antibody, 10 μg/ml); GH (100 ng/ ml)+ IgG (10 μg/ml, GH/IgG); IGF-I (100 ng/ ml)+ IgG (10 μg/ml, IGF/IgG); antibody to IGF-I (10 μg/ml, anti-IGF); GH (100 ng/ ml)+ anti- IGF (10 μg/ml, GH/anti-IGF); IGF-I (100 ng/ ml)+ anti- IGF (10 μg/ml, IGF/anti-IGF); no further additions (control). We repeated the experiment six times. Adding GH to the maturation medium increased cleavage rates at Day 3 compared to control (87.3±1.2%>83.9±1.2%; P<0.05) but had no effects on blastocyst development at Day 8. At Day 8, blastocyst development was greater ( P<0.01) for GH/IgG (24.8±2.5%) and IGF/IgG (33.7±2.5%) than for IgG (16.1±2.1%) and greater for IGF/IgG than for GH/IgG ( P<0.02). Blastocyst development at Day 8 did not differ between anti-IGF (20.4±1.8%) and GH/anti-IGF (24.1±1.9%) or IGF/anti-IGF (17.7±1.9%), but it was greater for GH/anti-IGF than for IGF/anti-IGF ( P<0.05). The Day 8 blastocysts of GH/IgG and IGF-I/IgG groups had a higher ( P<0.01) number of cells than the IgG group. The addition of anti-IGF-I eliminated the effects of IGF-I on cell number but did not alter GH effects. In conclusion, both GH and IGF-I stimulate embryonic development in cattle and GH effects may likely involve IGF-I-independent mechanisms.