The reverse transcription/polymerase chain reaction (RT-PCR) was used to amplify a 129-bp fragment of the mumps virus F gene from strains circulating in the Siena area from 1993-1995. The nucleic acid was amplified directly from the samples; no growth in cell culture was required. Nucleotide sequence analysis and the comparison with other virus strains enabled the typing of the detected viruses. There appears to be more than one lineage of mumps virus circulating at any given time in the same location. A PCR assay coupled with the sequencing of the 5' end of the F gene seems to be a convenient method for characterizing mumps virus strains. This method, useful in diagnosis, also appears to be suitable for epidemiological studies.