In eight consecutive adult heart surgery patients, serum concentrations of cefuroxime and gentamicin were studied during and after operation. Repeated doses of cefuroxime 1.5 g and gentamicin 80 mg were given. Intra-operative concentrations were deemed adequate (cefuroxime Cmin: 16-45 mg/l, gentamicin Cmin: 1.6-2.8 mg/l), and no differences (P = 0.05) could be demonstrated between elimination rates during and after open heart operation (cefuroxime T1/2 101 vs 111 min, gentamicin T1/2 191 vs 193 min).