Sera from patients with systemic infections caused by the opportunistic fungus Trichosporon beigelii have been shown to cross-react with anticryptococcal antibodies. We quantitatively compared the amounts of antigen produced and examined the expression of O-acetyl epitopes from 35 strains of T. beigelii isolated from deep and superficial infections. By counterimmunoelectrophoresis, 10 of 10 isolates from deep infections were positive for polysaccharide, compared with 7 of 13 isolates from superficial infections (P = 0.02). All 23 strains tested were positive for polysaccharide when screened by immunodot. By enzyme immunoassay, the cross-reactive antigen produced by deep isolates (n = 9) had a mean titer of 1:5,500. In contrast, superficial isolates (n = 22) produced significantly less antigen than the deep isolates (P < 0.001), with a mean titer of 1:700. Isolates from environmental sources (n = 3) were similar to the superficial isolates, with a mean titer of 1:600. The mean concentrations +/- standard errors of cross-reactive polysaccharide released by deep isolates and superficial isolates were 3.09 +/- 0.44 and 1.74 +/- 0.30 micrograms/ml, respectively, when measured by rocket immunoelectrophoresis (P = 0.02). O-Acetyl epitopes were detected on polysaccharide from 8 of 9 strains of T. beigelii isolated from deep sources, while only 2 of 12 superficial isolates expressed detectable O-acetyl epitopes (P = 0.01). Thus, while all isolates of T. beigelii tested were capable of producing glucuronoxylomannan-like cross-reactive antigen, pathogenic isolates produced significantly more antigen than superficial or environmental isolates. Furthermore, significantly more pathogenic isolates than superficial or environmental isolates expressed antigen that was O acetylated.