The region of the gyrA gene encoding nucleotides 72 to 557 in ten Salmonella typhimurium clinical isolates received from Vellore, India and six British clinical isolates of a number of Salmonella species has been sequenced. Those exhibiting a decreased susceptibility to 4-quinolone drugs (MICs of ciprofloxacin ranging from 0.128 mg/L to 1.0 mg/L) have been shown to possess a number of different mutations in this region of the gene (Asp-87 to Gly, Asp-87 to Asn and Ser-83 to Phe). The mutations Asp-87 to Gly and Ser-83 to Phe/Asp-87 to Asn have yet to be reported occurring in S. typhimurium.