PROBLEM: Recruitment to randomised trials is often difficult, and many important trials are not mounted because recruitment is thought to be "impossible." DESIGN: Controversial ProtecT (prostate testing for cancer and treatment) trial embedded within qualitative research. BACKGROUND AND SETTING: Screening for prostate cancer is hotly debated, and evidence from trials about the effectiveness of treatments (surgery, radiotherapy, and monitoring) is lacking. Mounting a treatment trial is controversial because of past failures and concerns that differences in complications of treatment but not survival make randomisation unacceptable to patients and clinicians, particularly for a trial including monitoring. STRATEGY FOR CHANGE: In-depth interviews explored interpretation of study information. Audiotape recordings of recruitment appointments enabled scrutiny of content and presentation of study information by recruiters. Initial qualitative findings showed that recruiters had difficulty discussing equipoise and presenting treatments equally; they unknowingly used terminology that was misinterpreted by participants. Findings were used to determine changes to content and presentation of information. EFFECTS OF CHANGE: Changes to the order of presenting treatments encouraged emphasis on equivalence, misinterpreted terms were avoided, the non-radical arm was redefined, and randomisation and clinical equipoise were presented more convincingly. The randomisation rate increased from 40% to 70%, all treatments became acceptable, and the three arm trial became the preferred design. LESSONS LEARNT: Changes to information and presentation resulted in efficient recruitment acceptable to patients and clinicians. Embedding this controversial trial within qualitative research improved recruitment. Such methods probably have wider applicability and may enable even the most difficult evaluative questions to be tackled.