Motivational interviewing is a client centred behavioural therapy foraddictive behaviours. It is an intervention designed to help all addicts,not just those ready to change. It is therefore suitable for use as anopportunistic intervention for clients whose main reason for contact maynot be their addiction. A pilot randomized controlled trial of home-basedmotivational interviewing by a specially trained midwife to help pregnantsmokers reduce their habit was performed in Glasgow from February 1997 toJanuary 1998. Did motivational interviewing take place? All 171 counsellinginterviews from 48 intervention clients were audio-taped. Forty-nineinterviews from 13 randomly selected clients were transcribed for contentanalysis. A rating scale established for feedback to trainee psychologistswas used by three experienced analysts. Thirty-two interviews were scoredindependently to validate the rating scale in this setting. More than 75% ofinterviews showed satisfactory motivational interviewing. Therapistutterances were motivational, and client responses included manyself-motivational statements. Few episodes of client resistance wererecorded. Rating took 160 mins per half hour interview. This instrumentprovided a valid measure of intervention quality for a randomizedcontrolled trial. It would not be practical to document process outsidea research environment.