An extensive skin testing program is part of the United States Naval Medical Command's infectious disease control effort. From 1980 to 1986, 2,306,533 skin tests, using five TU PPD, were performed on active-duty Navy and Marine Corps personnel, 0.97 percent of which were positive. A downward trend in positive tests was found with a high of 1.43 percent in 1980 and a low of 0.80 percent in 1983. Since 1984, the percentage of positive tests has remained the same or increased. Shore-based medical facilities around the world reported 1,491,646 skin tests with 1.07 percent positive; Navy ships reported 814,887 skin tests with 0.78 percent positive. PPD-positivity for ships in the Pacific area was higher (0.98 percent) than for ships in the Atlantic (0.62 percent). During this same period, the percentage of positive tests in Navy and Marine Corps recruits ranged from a high of 1.82 percent in 1981 to a low of 1.23 percent in 1986. Since 1984, the percentage of positive tests has remained relatively stable in recruits. The frequency of positive PPD tests found in this study is lower than the percentage positive (1.59 percent) found in active-duty Navy personnel in 1969 and the percentage positive (5.2 percent) found in a study of Navy and Marine Corps recruits between 1958 and 1969.