A human keratinocyte cell line (HaCaT) was analysed for plasminogen activator activity. By immuno-capture and immuno-inhibition studies we obtained evidence that HaCaT cells synthesize and secrete urokinase-type plasminogen activator (uPA) and tissue-type PA (tPA). Zymographic analysis by using fibrin agar indicator gels indicated that part of the PA activity in culture supernatants of the HaCaT line is complexed with putative PA inhibitors (PAI). Alkyl sulfates of different chain length were found to have a strong stimulatory effect on PA activity in HaCaT culture supernatants. Our findings are discussed in view of the known skin-irritating effects of alkyl sulfates in vivo.