Exposure of human cells in culture to chlorhexidine at concentrations equal to or greater than 0.004% resulted in impaired cellular function and/or cell death. Release of membrane bound 51Cr, inhibition of protein synthesis as measured by incorporation of 3H-leucine into protein-like material, and staining by trypan blue were seen as sequellae to exposure to 0.006% chlorhexidine for 3 hours. Lower doses were capable of inhibiting protein synthesis and releasing 51Cr, but did not result in staining of cells by trypan blue. Exposure of cells to 0.2% chlorhexidine for 30 seconds produced maximal suppression of protein synthesis and release of 51Cr.