With the paper by Kevin Fenton et al in this issue of STI (p 84)¹ we reintroduce the series planned to review research methodology as it might apply to research in sexually transmitted infections. The first article by the series editors Judith Stephenson and Abdel Babiker came out last August.² Additional articles will cover study size; cohort studies; case-control studies, survey methods; questionnaire design; mathematical modelling, selection of controls; qualitative research; and uses and abuses of geomapping software. We recognise that in addition to the common problems faced by all researchers, those working in STI face problems specific to this field. The series is aimed to help researchers overcome some of these. We invite suggestions for future articles.