Using a national county database, we examine the hypothesis of increasing spread of acquired immune deficiency syndrome (AIDS) in rural America. Data for county-level AIDS caseloads for the period 1982-1990 were obtained by contacting state health officials of individual states. Yearly and cumulative AIDS cases by county or health district were converted to rates with use of the 1986 population figures. The data were grouped into 3-year periods, 1982-1984, 1985-1987, and 1988-1990, and analyzed. The top 25 counties that had the highest rates of increase were identified, and their average population sizes were derived. Pearson's correlation coefficients between the rates of increase and county populations were also computed. The results corroborate data from previous studies based on selected regions and clearly point to an increasing spread in rural counties on a national basis. During 1982-1984, highly populated counties had the highest rates of increase in number of cases of AIDS, with the populations of the top 25 counties averaging 1.1 million. Between 1988 and 1990, the top 25 counties that had the highest rates of increase are mostly rural counties with an average population of 73,000. Not only are we presently faced with a much larger base of population infected with AIDS than before, the epidemic has also entered a dangerous phase of spreading to rural America where health care facilities are far less adequate than in urban areas.(ABSTRACT TRUNCATED AT 250 WORDS)