Abnormal pigmentation was found in the striatum, pallidum and substantia nigra of two unrelated patients. Both had suffered from debilitating joint disease; there was no evidence of a progressive neurologic disorder. The pigment was localized in astrocytes and had the histochemical and electron microscopic features of melanin. The tissue changes suggest an anomaly of catecholamine metabolism either endogenous or induced by a still unknown exogenous factor.