Fifty consecutive patients with allergic asthma and/or rhinitis in Madison. Wisconsin, were tested intradermally with a house dust extract (1:100) and with a Dermatophagoides farinae antigen (1:2000). The close relationship between the two skin test results (mite and house dust) suggests that both contain the same cross-reacting antigens and that mites make a major contribution to the antigens in house dust in Wisconsin.