Histologic examination of standard biopsy specimens from nasal mucosa were performed on 98 former and present employees at a nickel refinery and 61 controls. Histologic characteristics of the epithelium were graded blindly according to a point score table. The histologic scores were compared to certain epidemiologic data, such as the degree and duration of nickel exposure, duration of industrial work without nickel exposure, age, and smoking habits. High histologic scores were correlated to high nickel exposure, to the duration of this exposure, to age, and to industrial work not involved with nickel. One person with nasal carcinoma was detected in the nickel-exposed group. During the investigation period, three additional nasal carcinomas in former nickel workers were discovered and later included in the study. Furthermore, 18 cases of epithelial dysplasia were found in the nickelexposed group, but none among the controls. The cases with nasal carcinomas were or had been working with processes that gave an estimated high nickel dust exposure. All the individuals with epithelial dysplasia were nickel process workers.