To investigate furhter the problem of salivary transmission of type B hepatitis, salivas free of blood contamination from three HBsAg-positive carriers with chronic active hepatitis were examined by CsCl equilibrium density gradients and electron microscopy (EM). In the CsCl gradient HBsAg of whole salivas distributed in a band centered at 1.19gm/cm3 with a clearly defined shoulder at 1.24 gm/cm3; the HBsAg was found mainly in the mucous component. On EM examination, fractions from the 1.19 gm/cm3 peak contained spherical HBsAg particles of 22 +/- 3 nm diameter, whereas in the 1.24 gm/cm3 shoulder Dane particles 43 nm in diameter with 28 nm cores were found. Specific hepatitis B virus associated DNA-polymerase activity also was found in the 1.24 gm/cm3 shoulder where the Dane particles occurred and was absent from the saliva of healthy controls. When salivas were incubated for three hours at 37 degrees C the total amount of HBsAg diminished and the 1.24 gm/cm3 shoulder disappeared, probably as a result of endogenous degradation of the Dane particles and the free HBsAg. These findings clearly indicate that the hepatitis B viral particle is present in the saliva of chronic HBsAg carriers with active disease and further confirm that saliva is an important vehicle of infection.