Fifty-one chlamydial isolates from birds collected in Switzerland were classified by amplification and restriction analysis of the 16S-23S rRNA intergenic spacer region as Chlamydophila psittaci. The aim was to characterise a broad panel of chlamydial strains from birds and to apply and verify the methods of classification and differentiation described for chlamydial organisms. Two of the six known avian chlamydial serovars (A and B) were found by serotyping with monoclonal antibodies. One isolate was not typable. Digestion of ompA-PCR amplicons by AluI generated four distinct restriction patterns (genotypes A, B, F and G). Genotypes A and B correlated in most cases to serovars A and B, respectively. One serovar A isolate was verified as genotype B instead of A and one serovar B isolate belonged to genotype A. The non-serotypable isolate was of genotype F and one serovar A generated genotype G. OmpA sequences of one strain of each genotype were determined and compared to data bank entries. Amino acid sequences of genotype A and B strains corresponded well, showing more than 98.0% homology. The homologies of genotypes F and G sequences to genotype A strain were 82.0 and 83.0% respectively.