Cytogenetics results of three xenografted nasopharyngeal carcinomas (NPC) are reported. One (C15) was almost diploid and had only an isochromosome 1q, trisomy 2, and loss of chromosome X. The two other tumors, C17 and C19, were hypodiploid and had complex karyotypes with some variations. Nonrandom structural abnormalities of chromosomes 1, 3, 8, and 17 were observed. A correlation between a del(17)(p11-12) observed in C17 and loss of both alleles of p53 recently shown in this tumor is emphasized.