OBJECTIVE: To examine if the ultra-highly diluted homeopathic remedy Thuja 30C can ameliorate benzo(a)pyrene (BaP)-induced DNA damage, stress and viability of perfused lung cells of Swiss albino mice in vitro.METHODS: Perfused normal lung cells from mice were cultured in 5% Roswell Park Memorial Institute medium and exposed to BaP, a potent carcinogen, at the half maximal inhibitory concentration dose (2.2 μmol/L) for 24 h. Thereafter, the intoxicated cells were either treated with Thuja 30C (used against tumor or cancer) or its vehicle media, succussed alcohol 30C. Relevant parameters of study involving reactive oxygen species (ROS) accumulation, total glutathione (GSH) content, and generations of heat shock protein (hsp)-90 were measured; the cell viability and other test parameters were measured after treatment with either Thuja 30C or its vehicle media. Circular dichroism spectroscopy was performed to examine if Thuja 30C directly interacted with calf thymus DNA as target. For ascertaining if DNA damaged by BaP could be partially repaired and restituted by the remedy, 4′,6-diamidino-2-phenylindole staining was performed.RESULTS: Thuja 30C increased cell viability of BaP-intoxicated cells significantly, as compared to drug-untreated or drug-vehicle control. A minimal dose of Thuja 30C significantly inhibited BaP-induced stress level, by down-regulating ROS and hsp-90, and increasing GSH content. Thuja 30C itself had no DNA-damaging effect, and no direct drug-DNA interaction. However, it showed quite striking ability to repair DNA damage caused by BaP.CONCLUSION: Thuja 30C ameliorates BaP-induced toxicity, stress and DNA damage in perfused lung cells of mice and it apparently has no effect on normal lung cells.