Aqueous pharmaceutical solutions provide prosperous living conditions for microbiological agents. In order to eliminate these microbes, we use preservatives which can harm human cells as well. Their cytotoxicity is concentration-dependent and the aim of our study was to find how other pharmaceutical excipients modify the cytotoxic attributes of preservatives. We tested the following compounds: methylparaben, benzalkonium chloride, polysorbate 20, Labrasol® and hydroxyethyl cellulose. The MTT tests indicated that surfactants increase the cytotoxicity while polymers may decrease it in some cases.