Extrinsic contamination of propofol is thought to be a source of postoperative sepsis. Researchers studied growth of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans in propofol, thiopental and in a 1:1 propofol-thiopental mixture. All microorganisms were taken from standard stock cultures. Half of the samples were incubated at 20 degrees C and the rest were stored at 4 degrees C for 120 h. Growth of microorganisms in each solution was compared by counting the number of the Colony-Forming Units (CFUs) at 0, 3, 6, 24, 72 and 120 h. Propofol supported the growth of all four microorganims at both temperatures. In contrast, thiopental and the 1:1 propofol-thiopental mixture exhibited markedly bactericidal properties on E. coli, C. albicans and P. aeruginosa and bacteriostatic effect on S. aureus.