Mainstream (MS) and sidestream (SS) smoke of 3R4F reference cigarettes was simultaneously generated using a modified JB-2070i smoking machine and directed to the two different exposure carousels. Three target exposure concentrations within the range of commonly used in smoke toxicity studies were selected per WTPM (wet total particulate matter): MS smoke (500, 250, and 60 µg/L); SS smoke (130, 95, and 55 µg/L). The exposure duration was 1 hr for all exposure runs. CO (carbon monoxide), WTPM, nicotine, aldehydes (formaldehyde, acetaldehyde, acrolein, propionaldehyde, and crotonaldehyde), butt lengths, particle size (using cascade impactor and scanning mobility particle sizer), and environmental parameters (temperature and relative humidity) at the animal exposure nose-ports were measured. All data demonstrated high stability of the exposure system for the both MS and SS smoke with relative standard deviation ≤~10%. Most of constituent concentrations of the MS and SS linearly increased with the increase of the target WTPM exposure concentrations. SS smoke demonstrated significantly higher aldehyde content than MS smoke. MS particle size was stable for all three exposure concentrations, whereas SS particle size, significantly smaller than the MS smoke, tended to decrease with decreasing WTPM concentration. This may explain the increasing nicotine to WTPM ratio of the SS smoke with decreasing WTPM concentration. In summary, the study demonstrates stable and automated generation and monitoring of simultaneous exposure of MS and SS smoke up to 72 animals per each smoke type.