The concentration of molds isolated in 68 homes of allergic patients in southern California using the Andersen volumetric sampler varied from a minimum of 36 to a maximum of 5,984 isolate/M3 air sampled. The most frequently isolated included Cladosporium, Penicillium species. Alternaria, Sterile (Non-sporulating) Mycelium, Epicoccum, Aspergillus species, Aureobasidium and Dreschlera. Statistically significant higher mold isolates were associated with high shade and high levels of organic debris near the home and poor landscaping and landscape maintenance. Low concentrations of mold isolates were associated with the presence of a central electrostatic filtration system and good compliance with dust controls. The viable mold spore levels were lower in homes where the electrostatic filtration unit was operated continuously rather than intermittently. No statistically significant correlations could be made between indoor mold isolates and any of the following: number and age of the occupants, age and size of home, month of survey or the presence of indoor plants.