During the past decade, interest group participation in state supreme
courts has continued to increase, reflecting the increasing importance
of these courts as policymakers in the federal system. Groups partici
pate both as sponsors of litigation and as amici curiae, but little is
known about either role. The present analysis explores the success of
amici curiae in state supreme court decisions on the merits. Three me
thods of assessing the relationship between amici support and litigant
success are employed: their simple won/loss ratios, their success in
''matched pairs,'' and the relationship between amicus support and the
success of litigants in state courts in a multivariate logit model. A
ll three methods suggest that support from amici is significantly rela
ted to the likelihood of success of the supported litigants, regardles
s of whether amici support the appellant or the respondent.