Client language from a motivational interview (MI) and drug use outcome were investigated. Interview videotapes of 84 drug abusers were coded for frequency and strength of utterances expressing commitment, desire, ability, need, readiness, and reasons to change or maintain their habit. Cluster analysis of proportion days abstinent (PDA) revealed 3 groups: high PDA at intake and follow-up (3, 6, 9, 12 months; maintainers); low intake PDA/high follow-up PDA (changers); and low intake PDA/low to moderate follow-up PDA (strugglers). Distinct group patterns emerged for commitment strength (CS) during MI. Clients dishonest in checklist self-report exhibited CS similar to strugglers. CS for client evaluation of a change plan predicted outcome PDA. CS was predicted by strength of desire, ability, need, and reasons, but more strongly predicted outcome PDA, suggesting CS is a pathway for their influence on behavior.