This article documents design changes in Australian cigarettes since the adoption of a "low-tar" harm reduction strategy in 1966. It also determines the relative contributions of specific technologies to machine-tested tar and nicotine yields in 1980 and 1994, using data from tobacco industry documents. Our findings are consistent with a first generation of low-tar cigarettes, which relied primarily on filtration efficiency, being displaced by a second generation, which relied heavily on filter ventilation and were more attractive to consumers. In 1980, both tar and nicotine yields correlated most strongly with filter density (r=-.66, p<.01, and r=-.70, p<.01), whereas in 1994 both tar and nicotine yields correlated most strongly with percentage filter ventilation (r=-.97, p<.01, and r=-.95, p<.01). We also found that median percentage alkaloid content of tobacco rods rose from 2.16% in 1980 to 2.4% in 1994, despite median nicotine yield declining from 1.0 mg to.58 mg. These changes can be expected to reduce the utility of the FTC/ISO yield testing system.