BACKGROUND Previous Food and Drug Administration (FDA)-approved enzyme-linked immunosorbent assay testing of Dermatophagoides pteronyssinus diagnostic extracts showed potencies of 36% to 44% for 3 European extracts relative to the FDA standard (10,000 AU/mL). OBJECTIVE To compare biological activity of various European D pteronyssinus diagnostic extracts against an FDA-validated extract using quantitative skin prick tests. METHODS Six diagnostic D pteronyssinus extracts (1 reference extract, which was made up of 10,000 AU/mL of the FDA-approved extract; 3 European extracts; 1 US-Mexican extract, which is imported as raw material from the United States and sold in Mexico; and 1 Mexican extract) were tested during 2 skin prick test sessions as a concentrate and 2 serial 2-fold dilutions, in quadruplicate, on the backs of 19 patients with D pteronyssinus allergic rhinitis. The Wilcoxon test for linked random samples was used in each group to investigate whether the distribution of the reference extract differed from each of the test extracts to a statistically significant degree (test level alpha = .05). RESULTS Extracts showed good dose response in wheal size for the concentrate compared with the 2 dilutions (steep part of the curve). All 3 European extracts (2-sided asymptotic significance, P = .003, P = .009, and P = .01, respectively) and 1 Mexican (P < .001) extract were less potent than the reference extract. European extracts varied in potency from 5,400 to 6,126 AU/mL, the US-Mexican extract had a potency of 7,444 AU/mL, and the Mexican extract had a potency of 2,099 AU/mL. CONCLUSIONS Our study confirmed the results from previous in vitro testing. Various diagnostic extracts of D pteronyssinus used in Europe and Mexico are less potent than those used in the United States. Similar comparisons using therapeutic extracts would be of interest.