The essential oils ofRosmarinus eriocalyxwhich were produced from the leaves of six populations of plants collected in Algeria under different ecological conditions were analysed by GC and GC/MS. InR. eriocalyx36 compounds were identified, with camphor (32.3–37.0%), camphene (17.0–20.0%), a-pinene (15.2–18.2%) and 1,8-cineole (7.6–11.4%) as main components in all samples. In order to permit comparison, analyses were also conducted on the essential oil ofR. officinalisfrom Spain and Italy. Also in this case the principal component was camphor (35.3% and 17.7%), followed by 1,8-cineole (24.0% and 23.5%) and limonene (11.0% and 9.5%). It has been demonstrated that quantitative differences in α-pinene, β-pinene, 1,8-cineole and camphor exist when our results are compared with these previously published.