In order to obtain more insight in the general growth pattern of the Snell-mouse growth in length and weight of normal and dwarf Snell-mice before and during treatment with human growth hormone (hGH), porcine growth hormone (pGH) and L-thyroxine (T4) were studied. In normal mice the length velocity has a peak at 1 1/2 week of age and diminishes gradually therafter. In contrast the weight velocity peaks at 4 1/2 week. These differences result in a biphasic pattern of the length/weight relationship. Dwarfmice exhibit marked growth retardation at 2 weeks of age and growth arrest at 4 weeks. From birth on a marked difference in length velocity is observed, compared to the normals. This contrasts with the weight velocity, which discriminates at a later age (2-3 weeks). In the dwarfmice dose and age dependent growth occurred with all tested hormones. A combination of pGH and T4 shows a growth response which is equal to the sum of the effects of the hormones given separately. Doubling the dose of pGH after 12 weeks of treatment did not much influence the growth curve. However, addition of T4 induced a small but definite further height increment.