Latex beads coated with anti-Cryptococcus neoformans antibody were agglutinated by serum from a bone marrow transplant recipient having a disseminated infection caused by Trichosporon beigelii. The cryptococcal latex agglutination titer in the serum of the patient rose to 1:2,560 by the time of his death. Necropsy confirmed the disseminated Trichosporon infection and absence of C. neoformans. Cell wall extracts of the isolate of the patient and two additional strains of T. beigelii agglutinated anti-Cryptococcus-coated latex beads. The antigen in the serum of the patient and in the extracts responsible for the agglutination was not destroyed by proteolytic enzymes or heat. A single antigen reactive with rabbit anti-Trichosporon serum could be identified in the serum of the patient and the cell wall extracts by rocket immunoelectrophoresis and crossed immunoelectrophoresis. Rocket immunoelectrophoresis and indirect fluorescent-antibody staining demonstrated that anti-Trichosporon antibody recognized the capsular polysaccharide of C. neoformans.