Phthalic anhydride (PA) is widely used in the production of alkyd and unsaturated polyester resins. It has been reported that some workers exposed to PA have developed dermatitis, rhinitis and asthma. The authors intended to investigate the prevalence of PA induced allergic diseases and to develop preventive measures of occupational diseases. Forty-five male workers from PA production and handling were selected as an exposure group. Forty-four male workers not handling PA at the same factory were chosen as a reference group. A symptom questionnaire, doctor's examination, eosinophil count, serum-total IgE and PA-specific IgE were done on the subjects. There were no significant differences in age, educational level, tenure or smoking habits between groups. Most clinical symptoms were significantly more frequent among the exposure group than the reference group: sneezing(62.2 %), rhinorrhea(57.8 %), nasal stuffiness(53.3 %), coughing(44.4 %) and nasal itching(35.6 %) were the major symptoms among the exposure group (p<0.01, p<0.05). There were no significant differences in eosinophil count and serum-total IgE between groups but the mean level in PA-specific IgE, in the exposure group, was statistically significantly higher than the reference group (p<0.01). Abnormal rates of eosinophil count, serum-total IgE and PA-specific IgE were not significantly different from each other. The prevalence rate was 68.9 % (31 cases) for allergic rhinitis in the exposure group, statistically significantly higher than the reference group (p<0.01). The prevalence rate was 6.7 %(3 cases) for bronchial asthma and contact dermatitis in the exposure group, not more statistically significant than the reference group. In the exposure group, the prevalence rate for age, educational level, tenure, smoking habits and use of protective devices are not statistically significant. In PA-specific IgE, sensitivity is 10.8 %, specificity is 100.0 %, positive predictability is 100.0 % and negative predictability is 61.2 % when criteria point is 3.5 KU/l or above. As a result, it was recognized that the exposure group had a high prevalence of PA induced allergic rhinitis. Also, in diagnosis of PA induced allergic diseases, medical histories and specific symptoms were the most important where as eosinophil count, serum total IgE are the only indirect informations. PA-specific IgE has been needed to evaluate the meanings more.