The effect of temperature on pigment synthesis in adult and juvenile Himalayan mice was investigated. Since pigment synthesis only occurs in actively growing hair, adult mice were plucked to induce hair growth. The extent of darkening of the hair was recorded by photography against a reference scale. The presence of pigment granules in hair follicles was investigated histologically. Housing adult and juvenile mice at 15° C results in the synthesis of pigment in growing hair follicles whereas housing at 30° C results in the absence of pigment granules in the growing hair follicles.