Summer-type hypersensitivity pneumonitis (SHP), the most prevalent type of HP in Japan, is caused by seasonal mold contamination in the home environment. The causative agent of the disease is Trichosporon cutaneum. The fungus grows in warm, moldy, decaying organic matter, and scatters in the air from the colonizing places. The inhaled fungi sensitize susceptible patients intratracheally and induce the disease. Glucuronoxylomannan of the fungus has a potent antigenicity that causes granulomatous alveolitis. Assay of anti-T. cutaneum antibody is very useful to establish the diagnosis of the disease because the antibody activity is virtually positive in all cases of the disease. Elimination of T. cutaneum from the colonizing places prevents recrudescence. SHP, a new form of HP, had been considered to be peculiar to Japan, but the first case of SHP outside Japan was identified in Korea last year. Soon it will be recognized in many countries of temperate and tropical clime.