Two malignant mesotheliomas were studied by banding techniques. Both neoplasms had a hypodiploid stemline. Five and eight marker chromosomes, respectively, were included in the stemline karyotypes. Monosomy 14, monosomy 22 and a No. 13 with an interstitial long-arm deletion were deviations found in both neoplasms. In addition, closely located regions in No. 1 and No. 3 were involved in both tumors in the formation of other marker types with dissimilar morphology.