New Haven (Connecticut) has implemented a syringe tracking and testing system (SST) which provides rapid and relatively unobtrusive estimates of needle sharing, needle return rates and circulation times, and changes in the rate of HIV infection among needles distributed by the program. SST data, taken in conjunction with information from client surveys, can provide specific estimates of HIV prevalence among intravenous drug users, the incidence rate of new HIV infections, and the percentage reduction in HIV incidence resulting from the needle exchange program. Other aspects of needle-exchange programs that are important to document relate to the demographics of the clientele, entry into drug treatment, and the stability of the size of the intravenous drug-using population before and during needle exchange programs. 3 tables, 2 figures, and 14 notes