A cream formulation containing glycoalkaloids purified from the plant species Solanum sodomaeum L. is effective in the treatment of the malignant human skin tumours; basal cell carcinomas (BCCs), squamous cell carcinomas (SCCs) and the benign tumours; keratoses and keratoacanthomas. Histological analyses of biopsies taken before, during and after treatment give compelling evidence of the efficacy of the formulation. The treated lesions did not recur for at least 3 years after cessation of therapy. The observed complete regressions were; 20/24 for the BCCs; 5/6 for the SCCs; 23/23 for the keratoses; and, 9/9 for the keratoacanthomas. Biochemical, haematological and urinanalytical studies demonstrated that there were no adverse effects on the liver, kidneys or haematopoietic system during treatment. Normal skin treated with the formulation likewise was free from adverse histological or clinical effects. The data indicate that glycoalkaloids of this type are therefore potentially useful in the treatment of several types of human skin cancers.