In order to study the adaptation of hepatitis A virus (HAV) in cell culture, we examined the mutational events of the genome in early passages of HAV strain GBM propagated either in FRhK-4 cells (fetal rhesus monkey kidney-derived) or in human embryonic kidney (HEK) and human embryonic fibroblast cells (HFS) in relation to their growth characteristics. Sequence analysis of the nucleotide region encoding 2B, 2C, and the beginning of 3A as well as the nucleotide region encompassing the 5' noncoding region (5'NCR) of the genome was performed on consecutive virus passages after amplification of the viral RNA from the cell culture supernatant by antigen-capture PCR. By the 2nd passage of the GBM variants cultured in FRhK-4 or in HEK cells we found a mutation at nucleotide position 3889 (2B coding region) which results in an amino acid substitution from alanine to valine. Further mutations present in the 2B/2C region of the cell culture-adapted GBM variants differ from each other and occur after the 10th or even the 40th virus passage. Another early change, an in frame deletion of nine nucleotides in the 3A region, appeared in the 5th virus passage only in GBM cultured on FRhK-4 cells. This genome region showed different mutations in the virus passages on HEK and HFS cells. The 5'NCR of the cell culture-adapted GBM variants, in contrast, did not show any mutations before the 8th virus passage. The faster and more efficient growth of the HAV strain GBM during successive propagation on cell cultures seems to correlate with the appearance of mutations in the investigated genome regions.