In the present study, we analyzed 28 squamous cell carcinomas of the head and neck (SCCHN) for mutations in the coding region of TbetaR-II using 'Cold' SSCP and automatic DNA sequencing analyses. Twenty-one percent (6/28) of the SCCHN examined contained TbetaR-II mutations compared with patient-matched normal tissues. These alterations included five missense mutations (A:T-->G:C transitions in codons 250, 401, 448 and 488, and a G:C-->T:A transversion in codon 373), and a 38-bp deletion between nucleotides 1825 to 1862. In addition to these code-altering mutations, one case exhibited a silent mutation (A:T-->G:C transition in codon 451) and three cases contained one of two potential population polymorphisms (codons 354 and 389). In contrast to colon and gastric cancers exhibiting microsatellite instability (MI) or replication errors (RER+), no 'indirect' frameshift mutations were identified within a 10-bp polyadenine repeat present in the TbetaR-II coding sequence. All of the mutations in the present study occurred within the highly conserved serine/threonine kinase domain and represent the first report of such 'direct' TbetaR-II mutations in primary human tumors. In addition, we analyzed a subset of SCCHN and corresponding normal samples for TbetaR-II mRNA expression using semi-quantitative multiplex RT-PCR. Expression of TbetaR-II was decreased by 24% to 74% in 20 of 23 SCCHN (87%) compared with patient-matched normal tissues. Taken together, the results from this study suggest that alterations in the nucleic acid sequence and mRNA expression of TbetaR-II are prevalent events in the development of SCCHN, which may deregulate cell cycle control.