Groups of five male and five female F344/N rats were exposed to atmospheres containing 0, 0.6, 1.2, 2.5, 5, or 10 mg nickel subsulfide/m(3) (equivalent to 0, 0.44, 0.88, 1.83, 3.65, and 7.33 mg nickel/m(3)) 6 hours per day, 5 days per week for a total of 12 exposure days during a 16-day period.