In this multicenter study we evaluated the results of a previous study (part I) in a relatively large Dutch patient population, using the two previously tested allergens (house-dust mite and grass pollen) and two other standardized allergens (tree pollen and cat dander). The obtained skin test results were expressed as a histamine ratio and compared with RAST and clinical history (CH), The sensitivity and specificity were calculated at different cutoff values of the skin tests. The optimum cutoff values of 0.7 intracutaneous tests (ICT) and 0.4 skin prick tests (SPT) resulted in a predictive value for the detection of allergic sensitization of 83% (RAST) and 77% (CH), and 91% (RAST) and 86% (CH), for the ICT and SPT, respectively. As the ICT and SPT were performed in different centers, the results of these methods cannot be compared. No systemic side-effects of the skin tests were recorded. These results generally correspond well with the predictions regarding safety and predictive value of part I of this study, in which a limited number of patients was studied. In conclusion, through the use of a limited number of standardized allergens in a small group of patients, it may be possible to predict a safe and efficacious concentration for routine skin testing and to extrapolate from these results to other standardized allergens.