This study examines an approach to identifying patterns of treatment r
esponse over time. Treatment response profiles are identified by clust
er analyzing a repeated measure of patient performance collected at in
tervals during treatment. The procedure is demonstrated in Study 1 usi
ng monthly urinalysis results of 103 patients entering methadone maint
enance treatment. The internal, external, and face validities of deriv
ed treatment response profiles are evaluated. A logistic regression mo
del predicting treatment response is then constructed from intake vari
ables found to correspond with the treatment response profiles. Study
2 replicates the procedures on an independent sample. Treatment respon
se profiles facilitate the analysis of treatment response offering adv
antages over common measures of treatment outcome, such as performance
at follow-up, change in performance from treatment entry to follow-up
, or performance summed across treatment.