Hexon preparations of type 1, 2, 3, 5, 7, and 14 adenoviruses were treated with a water-soluble carbodiimide to cause the blocking of at least one antigen component. Comparative studies of native and CDI-modified hexons, showed the groupspecific component of all hexons to consist of at least two different components; one being CDI-resistant and the other one CDI-sensitive. In addition, a CD-Iresistant subgroup-specific component was found in type 3, 7, and 14 hexons. Animal immune sera did not always contain antibodies against both of the two group-specific components. CDI-treatment of hexons resulted in an increase in their isoelectric points from 4.9–5.4 to 6.4–7.1, as well as an observed reactivity with agar and some slightly acid proteins. The carbodiimide did not cause the formation of hexon complexes to occur. A new effective method designed to obtain highly purified hexon preparations by means of immunoadsorption is described.