Plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels were determined in Large White (LW) and Meishan (MS) female pigs at 80 and 185 days of age before and after an infusion of porcine GH. Plasma GH concentration declined with age and was similar in both breeds. Plasma IGF-I concentration did not differ between MS and LW pigs at 80 days of age. It increased with age in LW pigs whereas it remained almost unchanged in MS pigs. GH infusion led to an increase in plasma GH concentration and elicited a rapid and persistent rise in plasma IGF-I levels in both breeds. IGF-I response to GH was lower in LW than in MS pigs at 80 days, whereas the reverse was observed at 185 days of age. It increased with age in LW while it declined in MS pigs. The present results suggest the development of a GH resistance in MS pigs. This is likely associated with sexual maturity. Whether such GH resistance would also be observed in postpubertal LW female pigs remains to be investigated.