abstract essential oil (eo) yield and composition of five accessions of mentha longifolia (l.) l. (leaves) were determined throughout their vegetative cycle by gc-ms and gc-fid analysis. these accessions were selected based on tlc profiles of dichloromethane extracts from wild individuals. the profile rich in -terpinyl acetate and 8-acetoxy carvotanacetone has not been previously reported. the maximum value of eo yield was obtained in advanced flowering stage. the major composition changes were noted at the beginning of the vegetative cycle, whereas more stability was found during the flowering stage. thus, significant changes in the major compounds were found in some accessions: piperitone and piperitenone oxides, -terpineol acetate and 8-acetoxy carvotanacetone, which showed a considerable increase (6.0% to 20.1%) during the vegetative growth, the same way that pulegone and piperitenone oxide in other accessions. as biological activities depend on eo composition, the knowledge of its seasonal changes should be emphasized.