The problem in marketing research is a difficulty in gathering information either in the exploration phase or in the sampling phase. The traditional survey or interview includes certain constraints that any marketing researcher should try to overcome as completely as possible in order to approximate reality. The "in situ interview" attempts to overcome these constraints. It has the advantages of a completely verbal interview while allowing the interviewer to observe the purchasing decision first hand. After summarising the limits of traditional interviews, we shall present the "in situ interview".