An outbreak of aspergillosis with the death of six birds in the North Carolina Zoological Park R. J. Reynolds Forest Aviary in the spring of 1993 led to an investigation of the concentration of Aspergillus fumigatus spores in the air. No Aspergillus sp. was found in the facility through use of the drop plate method (gravitometric sampling) along with swab-sampling of selected surfaces within the exhibit and plating of food samples and nesting material onto petri dishes of nutrient media. A number factors that could stress the avian population were identified. These included excessive heat in the upper portion of the aviary due to the failure of an air handling system, a malfunctioning cooling tower, and large numbers of visitors to the facility (an average of 3,500/day). In addition, the outbreak occurred during a period of increased nesting behavior. Sampling of the fungal population of the air was conducted 1 year later, when no disease was noted, to compare the sensitivity of the commonly used drop plate method (open plates of nutrient media) with a volumetric impaction method (Andersen N-6 Air Sampler). The volumetric method delivered quantitative as well as qualitative data and exhibited more sensitivity for fungal spores of size similar to those of Aspergillus sp.