The suitability of viable and non-viable volumetric collectors as prevalence indicators for potentially allergenic airborne fungi was studied during 124 paired exposures of the Burkard (Hirst) spore trap and a modified, wind-oriented Andersen sampler. Overall, viable recoveries of several Cladosporium form species varied directly with microscopic spore counts (p less than or equal to 0.0001). However, as spore levels rose, culture plate data progressively underestimated prevailing concentrations (recoveries falling below 5% at levels above 500 spores/M3). Viable collections yielded low estimates of prevalence (20-40%) even at modest Cladosporium levels (less than 100 spores/M3) and substantially understated the abundance and regularity in air of several additional taxa. Spores typical of Penicillium and Aspergillus form species were not sought in spore trap deposits. Careful examination of these failed to reveal typical arthrospores or Fusarium macrospores despite substantial recoveries of corresponding growth in culture. Correlations in the occurrence patterns of arthrospore-forming and non-sporulating colonies with those of Coprinus and 'other basidiospores' (excluding Ganoderma) were noted.