Objectives: To explore current patterns of testing for genital chlamydial infection in primary care, and to identify practice characteristics influencing testing rates. Method: Aggregate numbers of chlamydia tests and results for each practice in Nottingham Health District were matched to practice characteristics. Age specific testing rates and diagnosed prevalence were calculated, and characteristics of the practice tested for association with chlamydia testing rates. Results: Most tests (63.1%) were performed on women over the age of 25, but the proportion of positive tests was highest in 15-19 year olds (13.3%) followed by 20-24 year olds (8.2%). A higher ratio of GP principals to female practice population was associated with higher testing rates and more chlamydia isolations, but the ratio of female GP principals to patients was associated with higher testing rates only in 20-24 year olds. Diagnosed incidence was greatest in more socioeconomically deprived practice populations, and this was not explained by higher testing rates. Men were rarely tested. Conclusion: Current testing practice in primary care does not reflect the known epidemiology of genital chlamydia infection. Practices with lower doctor-patient ratios do less testing, and measures to enable their active participation in the envisaged screening programme will be important in reaching all at-risk groups.C hlamydia tests have become available to primary care practitioners over the past decade, and in some districts are now widely used. Pilot primary care sites for the implementation of opportunistic testing for chlamydia have recently been announced, following pilot studies in which primary care was the largest contributor to testing. 1 However, in the absence of surveillance for sexually transmitted infections (STIs) in primary care, little is known about current testing practices in this important setting, and guidelines are not in general use. Although a number of practitioner surveys have been undertaken, 2-6 their results are subject to selection bias and social desirability bias, and they do not aim to provide complete descriptive information on testing patterns across a population.We undertook this study of testing patterns in the Nottingham Health District in order to identify who is currently being tested in primary care, in relation to the known epidemiology of genital chlamydia infection. We also aimed to identify practice characteristics associated with differing testing rates and positive rates, with a view to informing policy makers on likely problems in the implementation of the envisaged screening programme. METHODSThe setting was 119 general practices served by the Public Health Laboratory Service in Nottingham, UK. The laboratory processes all chlamydia samples for Nottingham Health District, of which approximately 40% are from primary care, 25% from GUM, 25% from other hospital settings, and 10% from family planning clinics. We were provided with an aggregated database of test numbers and diagnostic results for Chlamydia trac...