Tixocortol pivalate (TP) is a good marker for hydrocortisone allergy. The concentration of TP to be included in the standard series for patch testing has been the subject of debate. The objective of this study was to investigate the right concentration of TP to be included in the standard series for patch testing. 3747 consecutive patients with dermatitis were patch tested simultaneously with TP 1% and 0.1% in petrolatum at 9 centres in the UK from August 2004 to December 2005. Statistical analysis of the results was performed using STATISTICA, version 6 software. 41 patients had positive reactions of current or past relevance. 20 were positive for both concentrations, 13 positive only for TP 1% concentration, and 8 positive only for 0.1% concentration. Statistical analysis, using a two-tailed difference in proportions test, did not show a significant difference between the 2 concentrations (P=0.21). There was no statistically significant difference between the 2 concentrations of TP. The number of allergens that can be included in the standard series is limited for practical considerations. When testing for screening purposes, TP 1% is recommended.