The Texas Commission on Environmental Quality (TCEQ) has developed a unit risk factor (URF) for nickel based on excess lung cancer in two epidemiological studies of nickel refinery workers with nickel species exposure profiles most similar to emissions expected in Texas (i.e., low in sulphidic nickel). One of the studies (Enterline and Marsh, 1982) was used in the 1986 USEPA assessment, while the other (Grimsrud et al., 2003) is an update to an earlier study (Magnus et al., 1982) used by USEPA. The linear multiplicative relative risk model with Poisson regression modelling was used to obtain maximum likelihood estimates and asymptotic variances for cancer potency factors (â) using cumulative nickel exposure levels versus observed and expected lung cancer mortality (Enterline and Marsh, 1982) or lung cancer incidence cases (Grimsrud et al., 2003). Life-table analyses were then used to develop URFs from these two studies, which were combined using weighting factors relevant to confidence to derive the final URF for nickel of 1.7E-04 per íg/m3. The de minimis air concentration corresponding to a 1 in 100,000 extra lung cancer risk level is 0.059 íg/m3. The TCEQ will use this conservative value to protect the general public in Texas against the potential carcinogenic effects from chronic exposure to nickel.