An in vitro reproductive cell-based toxicity assay was developed using MLTC-1 (murine Leydig tumour cell line) in order to examine the reproductive toxicity of two novel nanopharmaceutical compounds, namely ethylene glycol mono allyl ether and poly(ethylene glycol) octa-functionalized polyhedral oligomeric silsesquioxane. Three commonly used cytotoxicity assays, namely the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide], MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] and Crystal Violet assays, were compared, and the MTT assay proved to be the most accurate and reproducible for the MLTC-1 cell line. The doubling rate of the MLTC-1 cells was 30+/-3.5 h and the optimal seeding density for the MTT assay was 20000 cells per well, and the optimized MTT assay utilized a 4 h cell adherence followed by incubation with 0.5 mg/ml MTT for 1 h. The intra- and inter-assay CV (coefficient of variation) values were 12.3 and 11% respectively. MLTC-1 cells only produce the reproductive hormone progesterone in response to hCG (human chorionic gonadotropin), which stimulated progesterone production dose-dependently from 0 to 100 m.i.u. (milliinternational units)/ml (2706+/-1118 ng/ml). H(2)O(2) as a negative control killed 100% of cells at 1000 microg/ml. The two nanopharmaceutical compounds were cytotoxic at concentrations > or =0.1 microg/ml, but hCG decreased cytotoxicity to > or =1000 microg/ml (P<0.001). hCG-stimulated progesterone synthesis afforded some protection against the cytotoxic effects of the two novel nanotechnology compounds; therefore doses < or =100 microg/ml and an exposure period of 1 h would be recommended for testing in in vivo animal reproductive assays.