We investigated the effects of smoking fewer cigarettes/day (CPD) on urinary levels of 1-hydroxypyrene (1-HOP), a biomarker of carcinogenic polycyclic aromatic hydrocarbon (PAH) uptake. We randomly assigned 151 smokers to either a reduction group or a waitlist group. In the reduction group, we measured urinary 1-HOP at two baseline intervals. Then, the smokers were expected to reduce their CPD by 25% in weeks 0-2, 50% in weeks 2-4, and 75% in weeks 4-6 and to maintain reduced smoking through week 26. In the waitlist group, four baseline measurements were taken and then the smokers joined the reduction group. Urinary 1-HOP was quantified at weeks 4, 6, 8, 12, and 26 after baseline. Statistically significant reductions in urinary 1-HOP were observed at most time points examined in groups of smokers who reduced to different extents. Reductions in the waitlist group were also generally significantly greater than baseline levels. The reductions in 1-HOP were usually modest (ranging from 14% to 35% in all groups and time points examined), which partially reflects the fact that there are sources of pyrene exposure other than cigarette smoke. Thus, cessation of smoking would only be expected to result in partial reductions of 1-HOP. The observed reductions in 1-HOP were not fully consistent with reductions in CPD probably due to uncontrolled dietary factors. Collectively, the results demonstrate that some smokers can achieve substantial reductions in 1-HOP, reflecting reduced uptake of polycyclic aromatic hydrocarbons, by reducing CPD, but there was not a consistent relationship between these parameters.