Previous genetic and pharmacological studies suggest that knockdown-resistance (kdr) to pyrethroid insecticides likely results from a mutation(s) in the para sodium channel gene. In this study, para sodium channel genes from an insecticide-susceptible German cockroach strain, CSMA, and a kdr-type German cockroach strain, Ectiban-R, were cloned and sequenced. Comparison of the nucleotide sequences of paraCSMA and paraEctiban-R revealed two nucleotide differences at nt 1491 and nt 2979, respectively. Only the difference at nt 2979 (G in paraCSMA and C in paraEctiban-R) resulted in an amino acid change (Leu993 in CSMA and Phe993 in Ectiban-R). Leu993/Phe993 is located in the highly conserved membrane-spanning segment 6 of domain II (IIS6). Furthermore, reverse transcription-polymerase chain reaction (RT-PCR) sequence analysis using another two insecticide-susceptible and one kdr German cockroach strain, revealed that C2979 was specifically associated with kdr resistant strains, whereas only G2979 was present in all susceptible strains. These results suggest that a single amino acid change from Leu993 to Phe993 is responsible for the kdr-type resistance in German cockroach.