Observed household curbside recycling behavior in 2,213 households in similar cities. In one, all recyclables were mixed together, and in the other, 4 types of materials were separated. As predicted, the commingled program (CMP) achieved a higher average weekly participation rate (58% vs 42%), and more households participated at least once in 8 consecutive weeks (90% vs 77%). The CMP also generated more gallons of recyclables (32.1 vs 5.5 per household per week). In the city with the CMP, there was a significant level of consistency in the frequency of household recycling participation across a 2-yr period; overall participation remained over 90%. High, medium, and low socioeconomic residential areas in both cities displayed some significant differences in participation and quantity recycled. Surprisingly, areas with volunteer recycling block leaders did not have higher levels of participation than comparable areas without block leaders.