The data derived in the study of Dermatophagoides pteronyssinus by microscopic and immunological assays (double radial immunodiffusion in 2 modifications and indirect rat mast cell degranulation) are provided. The immunochemical assays permitting the detection of mites in 93.3% of cases have been shown to compare very favourably with the microscopic techniques that make it possible to detect mites only in 41.7% of cases.