The actions and interactions of recombinant insulin-like growth factor-I and -II (IGF-I and IGF-II), alone or in combination with human GH on body growth and the growth of several organs were studied in the Snell dwarf mouse. IGF-I and -II stimulate to a similar extent sulfate incorporation into cartilage, and both IGFs increase body length and weight. IGF-II as well as IGF-I have clear effects on the size of the submandibular salivary glands, kidneys, and spleen. IGF-II, however, did not influence the weight of the lung, in contrast with IGF-I. GH treatment alone resulted in growth of the liver, whereas both IGFs were inactive. Surprisingly, IGF-II and, to a lesser extent, IGF-I inhibited GH-induced growth of the liver. Glycogen storage in the liver was decreased by treatment with IGF-II alone or in combination with GH, as shown by histological examination. It was not affected by GH, IGF-I, or GH plus IGF-I. Also, the size of the centrilobular hepatocytes was decreased by treatment with IGF-II and IGF-II plus GH; GH alone had a hypertrophic effect, whereas IGF-I or GH plus IGF-I had none. In contrast to GH, IGFs did not increase polyploidy. Treatment with IGF-II increased the level of IGFBP-3, as did IGF-I or GH treatment, as shown by Western ligand blotting. The IGFs appeared to have a greater effect on the induction of 38.5-kilodalton IGFBP-3 than GH, suggesting a different role in the regulation of glycosylation. In conclusion, IGF-I and IGF-II as well as GH have a stimulatory effect on general body growth and are effective in the stimulation of serum IGFBP-3, sulfate incorporation into cartilage, as well as the growth of specific organs in Snell dwarf mice. Both IGFs, alone or in combination with GH, show distinct effects on the growth of the liver with respect to several histological parameters, which require further exploration.