47 adenovirus strains related to Ad11, 14, 16, 21, 34, and 35 (including all subgenus B prototypes) were analyzed by DNA restriction analysis with Bam HI, Bgl II, Hind III, and Sma I. Typical fragments occurring in most of the strains were observed only with Hind III. Besides Ad3 and 7, 20 different genome types were distinguished. A pairwise analysis of comigrating fragments was performed for all genome types and summarized for the four enzymes. A medium rate of comigrating fragments (50 to 60 per cent) was found between Ad11, 14, 34, and 35 strains; Ad16 and 21 had 35 to 50 percent comigrating fragments. Within each group of closely related strains, Ad16 strains, Ad21 strains, and Ad34 + 35 strains showed a high rate (greater than 70 per cent) of comigrating fragments. Ad3 and 7 showed more comigration with Ad16 and 21 than with the others. Sixteen strains related to Ad21 were identical in their DNA restriction pattern and by serology. The relatedness determined by fragment comigration and by serology was compared by a quantitative estimate. The DNA relationship between Ad11 + 14 and Ad34 + 35 was not corroborated by serology. Ad21 was serologically related to Ad34 and 35, but not to Ad16; the opposite was found for DNA. The intermediate Ad21-16 showed a unique DNA pattern with some relation to Ad16.