Organisms of the Mycobacterium avium, M. intracellulare, and M. scrofulaceum (MAIS) group were recovered in significant numbers from 63 soil samples collected from the floodplains of 4 major rivers in the eastern United States: Hudson (NY), James (VA), Savannah (GA, SC), and Tombigbee (AL, MS). The mean numbers of M. avium-intracellulare, M. scrofulaceum, and MAIS-intermediate biovars recovered increased significantly from the Hudson to the James to the Tombigbee and Savannah soil samples, agreeing reasonably well with previous findings on MAIS distribution in eastern U.S. waters and with the geographic distribution of naval recruits reacting to PPD-B and PPD-G, which is higher in the southeastern United States. From the Savannah and Tombigbee rivers, soils were collected throughout their lengths. The number of total MAIS and biovars recovered from the different soil sites varied widely and showed no obvious trends. However, statistical analysis revealed a highly significant correlation between high numbers of MAIS recovered and high acidity of the soils. Other soil characteristics, such as high total organic matter, high conductivity, and reduced moisture, were only weakly, if at all, correlated with high MAIS numbers. Whereas the general distribution of MAIS in these soils of the Northeast (NY), mid-Atlantic (VA), and Southeast (GA, SC, AL, and MS) might explain the geographic distribution of the naval recruits reacting to PPD-B and PPD-G, the distribution of MAIS in soils along the stretches of the 2 southeastern rivers was not correlated with the county-by-county frequency of PPD-B reactive naval recruits in Georgia, South Carolina, Alabama, and Mississippi.