Becker (1983) hypothesized thatinterest groups compete strategically forinfluence with policy makers; thatimportant model has been assumed or ignoredrather than tested. This paper buildstheoretical and econometric frameworks thatcan test hypotheses about strategicbehavior when data on interest-groupactivity are limited and discrete. Itapplies those frameworks to data oninterest-group pressure regarding additionsto the U.S. endangered species list. Theresults do indicate that these interestgroups respond to costs and benefits, butdo not support the hypothesis that pressurefrom one interest group increases ordecreases with the pressure intensity of anopposing group.