The purpose of this study was to determine the role of the house dust mite. Dermatophagoides pteronyssinus (Dp) and Dermatophagoides farinae (Df), in allergic diseases on the island of St. Lucia. Dust samples were taken from living quarters of patients and hospital volunteers. The level of Df antigen in these living quarters was measured by RAST inhibition. All samples showed Df antigen within a large range of values. Prick tests were done to house dust mite and molds on 91 patients with suspected allergic disease with 63 (69%) reacting to at least one antigen. Of these, 56 (88.9%) reacted to one or both mites. House dust mite is a major allergen in St. Lucia.