We report on a 1,551-base-pair-long DNA sequence, encoding the variable region and parts of the flanking conserved regions of the human adenovirus type 8 (AV8) hexon, and a sequence comprising 1,404 base pairs, encoding the corresponding regions of the human adenovirus type 31 (AV31). Comparison of the hexon sequences showed that the major sequence changes were located in loops I1 and I2 of the hexon polypeptides which form the surface of the virion. We established a type-specific polymerase chain reaction (PCR), using a combination of a group-specific (general) primer, located in a conserved region of the hexon gene, and type-specific primers located in the region that encodes for loop I2 of the AV8 (subgroup D), AV31 (subgroup A) and AV40 and 41 (both subgroup F) hexon polypeptides. We performed PCR directly from several different clinical specimens or from isolates (AV31). Type-specificity was confirmed by restriction analysis. We also carried out several PCR directly from faecal specimens, using a group-specific primer pair and compared the sensitivity of PCR with that of electron microscopy and enzyme immuno assay.