Teicoplanin, a new glycopeptide antibiotic, has a serum half-life of 47 h and excellent activity against Gram-positive bacteria, including methicillin resistant staphylococci, making it a potentially useful drug for cardiac surgical prophylaxis. In two prospective randomized studies, we have compared it with a broad spectrum regimen of an aminoglycoside and flucloxacillin. In the first trial, teicoplanin (400 mg on induction of anaesthesia and 200 mg 24 h later), was compared with tobramycin (80 mg tds for three days) and flucloxacillin (500 mg qds for 5 days) in 314 patients. Teicoplanin prophylaxis resulted in a significantly greater number of sternal wound infections (P less than 0.01), due to Gram-positive bacteria. Furthermore, Gram-negative bacteria were responsible for more respiratory and urinary infections after teicoplanin prophylaxis. In the second trial, comprising 203 patients, the teicoplanin dose regimen was changed to three doses of 400 mg but this did not improve the rates of infection.