The p16INK4A and p15INK4B genes on chromosome 9p21 encode the p16 and p15 inhibitors of cyclin D/cyclin-dependent kinase 4 complexes respectively. Mutations and deletions of the p16INK4A gene have been found in melanomas and many other types of tumors. To assess the role of the p16INK4A and p15NK4B genes in tumorigenesis of the pituitary gland, 31 sporadic pituitary adenomas and 2 pituitary adenomas in familial acrogigantism were examined for loss of heterozygosity on 9p21-22 and screened for mutations in the p161NK4A and p15INK4B genes. To identify pituitary adenomas which had lost 9p21-22, pituitary adenomas were genotyped with markers flanking the p16INK4A and p15INK4B loci. The frequency of mutations in coding regions of the p16INK4A and the p15INK4B genes in pituitary adenomas was determined with polymerase chain reaction-single strand conformation polymorphism analysis and sequencing of variants. Of the 33 pituitary adenomas, two revealed loss of 9p21-22 sequences, but none of them had tumor-specific mutations. We conclude that mutations of the p16INK4A and p15INK4B genes are not required for tumorigenesis of the pituitary gland.