The efficacy of iodophor germicides containing different concentrations of available iodine against transient (inoculated) bacteria and the natural hand microflora was compared with chlorhexidine gluconate (2 and 4%) liquid detergent (Hibitane), non-germicidal soap and a tap water rinse. The tap water rinse was ineffective compared with all other treatments. Only 4% chlorhexidine gluconate liquid detergent and iodophor containing 0.75% available iodine were significantly better than the non-germicidal soap for reduction of transient bacteria, Escherichia coli and Pseudomonas fluorescens, that had been inoculated onto hands. These agents also caused a significant reduction in the number of 'natural' microorganisms released from hands after a standard 15 s hand wash. The low-concentration iodophor products and the product containing 2% chlorhexidine gluconate failed to give results significantly better than the non-germicidal control soap. Baird-Parker medium and standard aerobic plate counts were highly correlated (r = 0.82), so that for studies of Gram-negative bacteria inoculated onto hands as a transient microflora, counts on Baird-Parker medium give a reasonable indication of the natural (residual) hand microflora.