This paper describes an ongoing study into the quality of service provided by the Irish Revenue Commisioners' on-line tax filing and collection system. The Irish Revenue On-Line Service (ROS) site has won several awards. In this study, a version of the widely used SERVQUAL measuring instrument, adapted for use with on-line services, has been modified for the specific case of ROS. The theory behind this instrument is set out, the particular problems of evaluating revenue collecting on-line are examined and the rationale for this approach is explained.