For testing with sodium lauryl sulphate (SLS), measurements of transepidermal water loss (TEWL) and cutaneous blood flow with laser Doppler (LD) are considered to be the most reliable methods. The aim of this study was to determine which method of measurement should be preferred when conducting SLS testing under varying conditions. Patch testing with SLS at different concentrations and exposure times was performed. TEWL values were compared with those of LD. TEWL values showed distinct changes at low SLS concentrations and short application periods. By contrast, higher SLS concentrations were necessary to increase LD values. Short application of patches changed TEWL rather than LD values. When evaluating SLS patch testing by bioengineering methods, TEWL measurement appears to be more suitable for a test procedure that provokes mild skin reactions (SLS concentration <1%), whereas LD measurement is more appropriate to evaluate pronounced skin reactions (SLS concentration >or=1%).