Based upon the Framework Convention on Tobacco Control (FCTC), the World Health Organization (WHO) has recommended that health authorities disclose toxicological properties of cigarette mainstream smoke (MSS) obtained not only according to US Federal Trade Commission (FTC)/International Organization for Standardization (ISO) conditions but also by more intense conditions such as the Health Canada Intense (HCI) condition. This is because smokers are believed to smoke more intensely than machine smoking under the ISO regimen. Because there are no previous reports on the toxicological properties of MSS of Japanese cigarettes under the HCI condition, we determined nicotine and water contents by gas chromatography (GC-MS and GC/Thermal Conductivity Detector (TCD)) for three product lots each of the ten bestselling brands of Japanese cigarettes following the WHO protocol. One of the three lots of each MSS condensate was also resolved in dimethylsulfoxide and investigated by Ames preincubation assay using Salmonella typhimurium TA100, TA98, and YG1024 strains with and without metabolic activation (rat liver S9 mix). Nicotine and tar yields with the HCI regimen were higher than those with ISO, the latter being very close to the values described on the packages of each cigarette brand. Mutagenicity was mainly observed in TA98 and YG1024 with metabolic activation. Mutagenic activity of MSS with the HCI regimen was 1.4-9 times higher than that with the ISO regimen. Based on YG1024 with activation, high activities were observed in several “low yield” brands. The activity of “low-yield” brands with the HCI regimen was not always lower than that of regular-yield brands with the ISO regimen. These results suggest that “low yield” cigarettes do not result in reduced exposure or reduced risk to humans.