The fruits of Solanum incanum Linnaeus are extensively used in Kenya for the treatment of cutaneous mycotic infections and other pathological conditions. The therapeutic activity of the berries has been attributed to their content of solanine and related glycoalkaloids, which are saponins and cytostatic poisons. In the present study, however, a simpler more potent antimicrobial substance with a phosphorylated structure similar to the purine adenine was isolated from the berries. The crystals of this compound were effective inhibitors of the growth of gram-positive and -negative bacteria, yeasts, dermatophytes, and some pathogens of agricultural produce. High concentrations of the substance caused hemolysis of erythrocytes.