The different reactivity of black and white skin after exposure to sodium lauryl sulphate (SLS) has been investigated. 9 white and 10 black male volunteers entered the study. The tests were performed on the back at 3 sites: untreated skin, skin pre-treated with occlusion and skin pre-delipidized. Irritant reactions were elicited applying 0.5% and 2.0% SLS via Finn chamber patch tests and monitored by means of laser Doppler velocimetry (LDV), transepidermal water loss (TEWL) and stratum corneum water content (WC). Higher TEWL, LDV, and WC values were recorded for 2.0% SLS when compared to 0.5% SLS and baselines. Pre-treatment with short-term occlusion generally increased values, while delipidization produced flattening of the data more detectable in whites than in blacks. Significant TEWL differences for the two concentrations were recorded in whites for the occluded site (P<0.02) while in blacks in the untreated (P<0.04) and delipidized (P<0.03) sites. LDV revealed significant changes in the untreated and pre-occluded white skin (p<0.05 and 0.01, respectively). In blacks, the values were significantly different only in the pre-occluded skin (P<0.01). Water content correlated with the visual score and was greatly increased in sites with strongly positive reactions (P<0.01). It appears that there are significant differences in the modulation of irritation, in the behavior of water barrier function and of the erythematous response between black whites. Clinical correlations are discussed.