Assessments of quality of care using Senior Monitor in three matched wards for elderly patients were carried out on three occasions The first assessment was carried out in June 1987 as a trial of the measurement tool The instrument allows for a maximum score of 100 All three wards scored above 60, with two wards scoring above 70 Primary nursing was introduced in one of the wards in January 1988 and the assessment was repeated in June 1988 All ward scores were above 70, with one ward, not the primary nursing ward, scoring above 80 A third assessment was carried out in June 1989 Again, all three wards scored above 70 but this time the primary nursing ward scored 86, the highest ward score of the series The results for the sub-sections of the assessment are explored in the paper and issues about validity, reliability and inter-rater reliability are discussed It is argued that Senior Monitor is a useful tool for assessing changes in the quality of care delivered to patients in wards for the elderly but that its full value only becomes apparent with repetition over an extended time period It may be less appropriate for assessing the impact of a change in the organization of care, not because of any inherent fault in the test but because the very process of using it makes staff look at their practice more critically It is this critical re-appraisal rather than the change in organization per se which stimulates the improvement in the quality of care