The species Allium neapolitanum Cyr. of the Section Mollium G. Don ex Koch is a common plant found in the Croatian Adriatic region as well as in a wider area along the coast and on the Adriatic islands /Table 1). In these localities, fifty plants from nine populations were collected and karyologically examined. The number, size and shape of mitotic chromosomes and their behaviour in meiosis were determined. Out of the polyploid series 2n=14, 21, 28 and 35 we found only the 5x level with 2n=35 and aneuploids with 2n=27, 30, 31, 32, 34, 36, 39 and 40 (Tables 1 and 2). The size of metaphase chromosomes ranged from 8.40 to 14.00 pm, from the shortest to the longest one (Table 3). The chromosomes were of meta- and submetacentric shape (only rarely of subacrocentric shape). Their number varied from karyotype to karyotype. Two chromosomes from group 31-34 (Table 3) showed secondary constriction next to the centromere, and they are known as nucleolar chromosomes. They have been named, according to this species, chromosomes of the »neapolitanum« type (Fig. 1, arrows) (Ved Brat 1965, cited from Kol- lmann 1973). Their number varies, and in alternative series it is smaller or greater than two. The variability of the karyotype was confirmed in meiosis. Irregular pairing of chromosomes was noted, as well as the appearance of uni-, bi-, tri- and multivalents, with a greater proportion of tri- and multivalents (Fig. 2). They separate into 17 and 18 chromosomes as well as in other ratios. Apart from uneven distribution of chromosomes, micronucleoli in the pollen grains also varied in number, indicating that some chromosomes or their fragments were not incorporated into new pollen nuclei. Despite such a course of meiosis, there was reproduction of the seed found in plants from cultivated and natural populations. The results concerning seed germination and germination of young bulbs are shown in Table 2. It follows that the species A. neapolitanum has a variable karyotype, which is manifested by a decreased or increased number of chromosomes, as compared to the most common karyotype, 2n=35 chromosomes.