Two types of B-chromosomes (acrocentric and submetacentric) were observed in the population ofAllium sphaerocephalonL. (Liliaceae) analyzed in this report. The submetacentric B-chromosome is an iso-B and the acrocentric B displays nucleolar activity. The B-chromosomes of this species caused a significant increase in the between-cells variance of chiasmata. The possible origin of these B-chromosomes is discussed in relation to several detected chromosome rearrangements (reciprocal unequal translocation and centric fission).