Local reactions during and after i.v. injection of two different formulations of diazepam were studied. Two-thirds of the patients felt pain during the injection. Verified or probable thrombophlebitis occurred with increasing frequency following operation, indicating a late onset. One month after discharge, 29% of those who had received diazepam in glycoferol-alcohol-benzoic acid complained of tender injection sites, compared with only 10% of the patients who received diazepam in cremophor EL. The difference is significant, indicating an influence of the solvent system