Domestic mites Dermatophagoides pteronyssinus, Dermatophagoides faringe and Blomia tropicalis house dust allergen levels in Cartagena were investigated. Dust samples were collected monthly from the homes of twenty asthmatic patients in Cartagena having allergy to these mites, using a portable vacuum cleaner throughout a 12-month period. The major allergens from D. pteronyssinus and D. faringe, Derp 1 and Der f 1 respectively, were determined by immunoassay using monoclonal antibodies. D. pteronyssinus and B. tropicalis total allergen levels were determined by RAST inhibition assay. The highest Derp 1 mean level in mattress samples was 109.49 nglg dust detected in August and represented more than twice the lowest levels (50.3 ng/g) detected in November. Derf 1 was detected in only three floor-dust samples. The highest levels of D. pteronyssinus allergens in mattress samples were detected during the months of May, June, July and August and the lowest levels from December to April. The highest levels of B. tropicalis allergens in mattress samples were detected in June, July and August and the lowest levels during September. The allergen levels in mattress-dust which were correlated with floor-dust levels were significantly higher than the latter (pc 0.0001). There was a good correlation between B. tropicalis and D. pteronyssinus allergen levels and absolute humidity. This study describes the presentation of minimal variation, throughout the year, in allergen levels from domestic mites in a tropical environment, and that B. tropicalis allergen levels are high and constant. Patients allergic to domestic mites in Cartagena are exposed throughout the year to an important allergenic load.