Acinetobacter type strains and isolates from wastewater treatment plants were differentiated by PCR fingerprinting. On the first level, PCR fingerprinting with two tRNA-gene specific primers (T5B and T3A) was used for the identification of species (genospecies 1 to 17). On the second level, a single arbitrary primer (DAF 4) was employed for strain differentiation. Upon comparison of Acinetobacter type strains with 28 sewage sludge isolates, 2 could be classified as belonging to A. johnsonii, 8 isolates could be classified as A. lwoffii, 8 could be classified as A. baumannii, and 9 isolates were very closely related to the Acinetobacter species A. junii; only 1 isolate could not be classified as one of the Acinetobacter type strains. The PCR fingerprinting method was found to be a reproducible and fast method for differentiation and identification of Acinetobacter isolates. Because of some resulting discrepancies compared with previously described identification schemes, e.g., DNA-DNA hybridization methods, the original identification experiments should be repeated and the results should be reassessed.