An analysis of cases of possible nephrotoxicity from cephaloridine (96) and cephalothin (63) reported over the last 10 years shows that in the majority of cases the toxicity was associated with either excessive dosage or previous renal functional impairment without appropriate dosage reduction. Other factors found frequently and thought to predispose towards toxicity are: the concurrent use of other potentially nephrotoxic antibiotics, especially gentamicin or the diuretic frusemide; the presence of intercurrent severe drug allergy and factors leading to temporary reductions in renal clearance such as surgical operations, dehydration and shock