A series of RFLP and isozyme markers were followed in the progenies of two alien addition lines of Brassica campestris-oleracea. One of the lines, carrying the C genome chromosome 4 as the alien chromosome, was surveyed for six markers. Fifty-four percent of the plants carrying alien chromosomes displayed all the expected makers, whereas the rest had one to five markers missing. The second line for C genome chromosome 5 displayed a similar behavior when surveyed for three markers. All three markers were transmitted together in 46% of the plants carrying alien chromosomes, whereas the rest carried only one or two of the markers. The loss of markers was associated with reduced chromosome size caused by deletions. The observed chromosome deficiencies permitted deletion analysis for a rough physical mapping and ordering of the markers on the two C genome chromosomes. The deletions observed may represent another mechanism for molding the chromosomes of the Brassica genomes during their evolution.