Although human sensitization to basidiomycete Ganoderma has been reported in New Zealand, North America and Europe, hypersensitivity due to this fungi is not known in India, in spite of its prevalence in the atmosphere. We have studied the atmospheric concentration of Ganoderma in different localities within Delhi and the sensitization level to this fungi amongst the Indian population. Aerobiological sampling, using a Burkard personal slide sampler, was carried out in Delhi for 2 consecutive years (October 1989-September 1991). The sampler was operated at 10 day regular intervals for 10 min to trap the spores. The peak season for Ganoderma is recorded from July to September with highest average monthly catch of 336 spores/m3 in September 1991 from south Delhi. Antigenic extracts were prepared from both, the spores and whole body of Ganoderma lucidum. The results of intradermal skin tests conducted on 172 patients revealed that 28.48% and 17.44% of patients showed marked skin reactivity to spore and whole body extracts, respectively. A significant correlation (r = 0.963, P < 0.01) was found between intradermal and skin-prick tests. More than 80% of the intradermal test positive patients had significantly (P < 0.01) elevated IgE antibodies to the fungi in question. Thus, sensitization to Ganoderma lucidum has been reported for the first time in the atopic population of India.