The performance, economics and acceptability to users of the INSPEC SDI system were investigated in this study. The effect that provision of an SDI service might have on the information-use habits of users was also studied. The sample group of users consisted of 600 individuals of whom 540 were drawn equally from: universities and colleges, government research establishments, and industrial firms. The remaining 60 were small groups of people having common information requirements. A corresponding sample of 600 people was used as a control group. The SDI operation was designed to provide a weekly service to users. All of the methods used to operate the SDI system and the problems encountered are discussed in some detail. The users comments on the service are also included. (Volumes II through V are: LI004068 through 004071.) (Author/NH)