The number and size of the chromosomes in the Sideritis L. genus which belongs to Hesiodia (Benth.) section were studied using the Image Analysis System. Chromosome number was determinated as 2n=30+0-2B in S. lanata L., 2n=28+0-3B in S. romana L. subsp. romana, 2n=28+0-4B in S. curvidens Stapf., 2n=16+0-2B in S. montana L. subsp. montana and 2n=18+0-3B in S. montana L. subsp. remota (d'Urv.) P.W.Ball ex Heywood. The chromosome lengths in these taxa were found to vary from 0.37 mu m to 1.33 mu m.