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Point mutations in the voltage-gated sodium channel gene involved in knockdown resistance to DDT and pyrethroid insecticides have been described in several insect species. In the malaria vector Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) two mutations have been identified. The first, consisting of a leucine–phenylalanine substitution at amino acid position 1014, is widespread in West Africa. The second, a leucine–serine substitution at the same position, has to date only been detected in western Kenya. Analysis of the kdr polymorphism in a sample of 106 An. gambiae s.s. of the rDNA S-form/Type I collected in Libreville (Gabon) surprisingly revealed the presence of both East and West African kdr mutations with frequencies of 63% and 37%, respectively. No wild-type alleles were detected and there was an excess of heterozygous genotypes (P = 0.04). In addition, an inconsistency was found during the kdr genotyping procedures by polymerase chain reaction, which could have lead to an underestimation of resistance alleles. The implications of these findings are discussed.