Imagine that 90 percent of all people living with H.I.V. were diagnosed and treated with drugs. Would that be sufficient to end the AIDS epidemic?

Scientists tried to answer the question i n three enormous studies published on Wednesday in the New England Journal of Medicine. Instead of simply urging people to get testing and treatment for H.I.V., health workers in five African countries went door to door, or set up mobile sites, offering tests for H.I.V., tuberculosis and other diseases to everyone in certain communities .

Anyone who tested positive for the infection was set up with clinic appointment to receive antiretroviral drugs. Then investigators assessed whether these efforts made any difference in the number of new H.I.V. infections in those communities.

Results from three of the studies suggest that the strategy comes nowhere near bringing the rate of new infections with H.I.V., or incidence, down to zero. But all of the studies showed that incidence dropped by about 30 percent, and one found a decrease in H.I.V.-related deaths.