The human fetal pancreas (HFP) is a potential source of insulin-producing B-cells for transplantation to insulin-dependent diabetic patients. We recently described a technique for culturing HFP tissue in vitro which results in the development of islet-like cell clusters (ICC). These clusters exhibited (pro)insulin biosynthesis and a modest rate of insulin secretion, and immunocytochemical staining indicated the presence of insulin-positive cells in the cell clusters. In this study this technique was used to evaluate the effects of the addition of 1000 micrograms/L GH to HFP cultured in medium RPMI-1640 plus 10% human serum. ICCs developed in 21 of 33 consecutive cultures. GH increased the yield of ICC by 35% compared to explants supplemented with human serum alone. The insulin content of the ICCs also was increased, but the size of individual ICCs was not affected by GH, as reflected by an unchanged DNA content. GH also caused increased insulin release when the ICCs were stimulated with 16.7 mM glucose plus 5 mM theophylline. However, (pro)insulin biosynthesis was not affected by the addition of GH. These results suggest that GH stimulates the formation of both ICCs and insulin production within the explants. These observations are relevant both for the production of human fetal B-cells intended for transplantation into insulin-dependent diabetic patients and for our knowledge of the growth regulation of the HFP B-cell.