abstract the chemical composition and antimicrobial activity of the essential oils isolated from four lamiaceae [thymbra capitata (l.) cav., origanum vulgare l. subsp. hirtum (link) ietsw., rosmarinus officinalis l. and satureja cuneifolia ten.] harvested at three different vegetative stages, spontaneously growing in the south of puglia, towards gram-(+)ve and gram-(-)ve bacteria and pathogenic yeasts were evaluated. the four oils were analyzed by gc-fid and gc/ms, and exhibited similarities and differences with respect to data reported in the literature. specifically, t. capitata and o. vulgare subsp. hirtum oils were found to be rich in thymol (60.9-67.5% and 29.8-56.8%, respectively) and r. officinalis oil had large amounts of 1,8-cineole (8.0-51.3%) and -pinene (3.9-31.4%). the composition of the oil of s. cuneifolia varied most of all, its main constituents being linalool (9.6-32.7%), borneol (12.9-24.0%) and -pinene (9.5-11.7%). each of the oils was found to possess some antimicrobial properties using the agar diffusion method. the effectiveness and behavioral specificity varied from one species to another, and within each species, in relation to the vegetative period and the microorganism tested. the most effective oils were those of o. vulgare subsp. hirtum and t. capitata. the latter was also biologically active towards p. aeruginosa which was not sensitive to either r. officinalis or s. cuneifolia oils. key word index: thymbra capitata origanum vulgare subsp. hirtum rosmarinus officinalis satureja cuneifolia lamiaceaeessential oil composition-pinene-terpinenep-cymene1,8-cineolelinaloolborneolthymolantimicrobical activity