An in vivo sulfur mustard (HD) vapor exposure model followed by bronchoalveolar lavage was developed previously in this laboratory to study biochemical indicators of HD-induced lung injury. This model was used to test two treatment compounds--niacinamide (NIA) and N-acetyl cysteine (NAC)--for their ability to ameliorate HD-induced biochemical changes. Anesthetized rats were intratracheally intubated and exposed to 0.35 mg of HD in 0.1 ml of ethanol or ethanol alone for 50 min. At the beginning of the exposure (t = 0), the rats were treated with either NIA (750 mg kg(-1)) or NAC (816 mg kg(-1)), i.p. At 24 h post-exposure, rats were euthanized and the lungs were lavaged with saline (three 5-ml washes). One milliliter of the recovered lavage fluid was analyzed for cellular components. The remaining fluid was centrifuged (10 min at 300 g) and the supernatant was assayed on a Cobas FARA clinical analyzer for lactate dehydrogenase (LDH), gamma-glutamyltransferase (GGT), albumin (ALB), total protein (TP) and glutathione peroxidase (GP). The HD alone and HD+NIA treatment caused significant increases in all of the biochemical parameters compared with control levels. The NAC treatment yielded LDH, ALB and TP values that, although elevated, were not significantly different from the control. The GP levels were significantly higher than the control but significantly lower than the HD alone levels, indicating some protection compared with the HD alone group. The GGT levels were unaffected by NAC compared with HD alone. Cytological analysis of lavage fluid showed that the percentages of neutrophils were 5.3 +/- 1.0 (mean +/- SEM) for control, 46.6 +/- 4.5 for HD, 31.4 +/- 4.7 for HD + NIA and 21.6 +/- 4.7 for HD + NAC, respectively. The neutrophil counts were significantly higher for the three HD-exposed groups vs controls; however, the NAC-treated group had neutrophil counts lower than HD alone, indicating decreased inflammatory response. These results show that NAC may be useful as a potential treatment compound for HD-induced lung injury.