We have analysed protein coding and intergenic sequences in the Borrelia burgdorferi (the Lyme disease bacterium) genome using di erent kinds of DNA walks. Genes occupying the leading strand of DNA have signi cantly di erent nucleotide composition from genes occupying the lagging strand. Nucleotide compositional bias of the two DNA strands re ects the aminoacid composition of proteins. 96% of genes coding for ribosomal proteins lie on the leading DNA strand, which suggests that the positions of these as well as other genes are non-random. In the B. burgdorferi genome, the asymmetry in intergenic DNA sequences is lower than the asymmetry in the third positions in codons. All these characters of the B. burgdorferi genome suggest that both replication-associated mutational pressure and recombination mechanisms have established the speci c structure of the genome and now any recombination leading to inversion of a gene in respect to the direction of replication is forbidden. This property of the genome allows us to assume that it is in a steady state, which enables us to x some parameters for simulations of DNA evolution. c © 1999 Elsevier Science B.V. All rights reserved. PACS: 87.14.G; 05.10-a