Objective: Reporting guidelines call for descriptions of control group support in equal detail as for interventions. However, how to assess the active content (behaviour change techniques (BCTs)) of treatment-as-usual (TAU) delivered to control groups in trials remains unclear. The objective of this study is to pre-test a method of assessing TAU in a multicentre cost-effectiveness trial of an HIV-treatment adherence intervention. Design: HIV-nurses (N = 21) completed a semi-structured open-ended questionnaire enquiring about TAU adherence counselling. Two coders independently coded BCTs. Main outcome measures: Completeness and clarity of nurse responses, inter-coder reliabilities and the type of BCTs reported were examined. Results: The clarity and completeness of nurse responses were adequate. Twenty-three of the 26 identified BCTs could be reliably coded (mean κ = .79; mean agreement rate = 96%) and three BCTs scored below κ = .60. Total number of BCTs reported per nurse ranged between 7 and 19 (M = 13.86, SD = 3.35). Conclusions: This study suggests that the TAU open-ended questionnaire is a feasible and reliable tool to capture active content of support provided to control participants in a multicentre adherence intervention trial. Considerable variability in the number of BCTs provided to control patients was observed, illustrating the importance of reliably collecting and accurately reporting control group support.