A series of BASIC programs is described to allow entry, validation and checking of coded lithological descriptions, additional prose-form notes and quantitative geotechnical data to a hand-held portable computer during on-site logging of geological drill holes for engineering purposes. The programs also permit the production of a written borehole log, in the field if necessary, along with tabulations of geotechnical data and a comprehensive graphic representation of the drill hole. Use of such a system avoids some of the errors that may arise in procedures which involve transcription from written notes in a later keypunch operation. The information can be transferred from the portable unit to an office-based facility, when required, for further processing by a more comprehensive installation.