Experimentally, inorganic, sulfated nickel compounds (Ni2+) have been shown to produce histological lesions in the nasal mucosa of rats, more specifically, atrophy of the olfactory epithelium. The present project was designed to assess the effects of inhalation of nickel sulfate hexahydrate on behavioral, histological, and neurochemical aspects of the olfactory system. Male Long-Evans rats were exposed to either background air (control) or 635 micrograms Ni/m3 for 16 consecutive days, 6 hr/day. Exposure resulted in selective lesions to the olfactory epithelium. The number of bipolar sensory receptor cells was slightly reduced and there was a significant decrease in the thickness of the olfactory epithelium. This was due primarily to a significant loss of the sustentacular cell population, with a thinning of the apical cytoplasm, concomitant with a reduction in the number of microvilli at the surface of these cells. Significant decreases in carnosine level, consistent with the nickel sulfate exposure, were observed. However, there were no changes in olfactory function as measured by either absolute threshold or two-oder discrimination tasks.