In the frame work of the European project EPIQR (energy performance, indoor air quality, retrofit), European apartment buildings were investigated with a newly developed tool called EPIQR. This tool is aimed at assessing information on refurbishment and retrofitting needs of apartment buildings. This package is, however, not only meant to identify the possible refurbishment/retrofitting needs but also to identify the possible improvements that can be made to result in a better indoor environment and a lower energy consumption. As part of the EPIQR tool (a user-friendly software programme), procedures and methods were developed to be able to investigate indoor environment quality (IEQ) in apartment buildings. Among others a questionnaire was developed. In this paper the methods and instruments related to IEQ developed for EPIQR are described and the results of the field study in the apartment buildings are reported and analysed [P.M. Bluyssen, EPIQR: IEQ part of EPIQR from 1 June 1996 to 1 June 1998, TNO Report 98-BBI-R0844, May, 1998]. (C) 2000 Elsevier Science S.A. All rights reserved.