To evaluate the effects of dilution and filtration on the particle size of tobacco smoke, a cyanoacrylate fixation technique has been applied directly to smoke issuing from a cigarette. This fresh, undiluted smoke has appreciable numbers of particles with diameters less than 0.1 and relatively few particles with diameters greater than 0.5 micrometer. For a middle puff on an unfiltered tobacco cigarette, the median and mass median diameters are 0.20 and 0.32 micrometer. The experimental method involves the injection of cyanoacrylate vapor directly into the issuing smoke stream, collecting a sample of fixed particles on a membrane filter, and the use of image analysis to separate, size and count individual particles. Aging of undiluted smoke for up to 1.4 seconds essentially doubles the number and mass median diameters and decreases the particulate concentration in line with coagulation theory. Different puffs on unfiltered cigarettes have little effect on the size distribution and particulate concentration. Addition of a filter removes both larger and smaller particles, and tends to skew the distribution to smaller sizes. The reduction in particulate concentration in filtered smoke is as expected from nicotine removal efficiencies. Filter dilution tends to skew the size distribution to larger sizes, while tobacco column dilution has no great effect. Particulate concentration correlates well with overall dilution levels.