Three patients, in whom tumour overkill by cytotoxic treatment, including high dose methotrexate with folinic acid rescue, resulted in the 'phosphate shower syndrome' (hyper-uricaemia, hyperkalaemia and hyperphosphataemia with hypocalcaemia and tetany, with metabolic acidosis and acute renal impairment) are described. Severe methotrexate toxicity occurred in two of these patients. High dose methotrexate would appear contra-indicated in situations where massive tumour lysis is possible.