Attempted to modify adult littering behavior in a naturalistic setting: the football stadium. Four different treatment strategies were used: (a) an operant contingency in the form of a positive reinforcement procedure; (b) 2 prompting procedures, a positive prompting and a negative prompting strategy; and (c) a litterbag-only condition. The dependent variable was defined as the weight of nonreturned litter. Treatment procedures were implemented twice in 2 consecutive football games and contrasted with no-treatment conditions. "Treated" Ss were 200 nonuniversity season-ticket holders in each of 6 sections of the stadium. Findings revealed a highly significant main effect of treatment, which was responsible for a 45% reduction in the amount of litter in the treated sections of the football stadium. There were no significant differential effects between the different treatment strategies. Results are discussed in relation to laboratory research on littering in children and with a perspective toward future operant research in the area of pollution behavior.