OBJECTIVE: The adenylyl cyclase system plays an important role in the control of both thyroid follicular and anterior pituitary cell function. Activating mutations affecting important pathway components such as the TSH receptor and Gsalpha occur in the majority of autonomously functioning thyroid nodules. Only a small proportion of other types of thyroid tumours, however, have been reported to harbour these mutations. Activating mutations of Gsalpha have been reported to occur in up to 40% of pituitary somatotroph adenomas. As the majority of cold thyroid nodules and pituitary tumours are unaffected by these mutations, we have investigated the possibility of activating mutations occurring in protein kinase A (PKA), which is another key component of the adenylyl cyclase pathway. DESIGN: Genomic DNA and cDNA were analysed for the presence of PKA Calpha mutations by allele-specific oligonucleotide hybridisation and single strand conformation polymorphism analysis. PATIENTS: A total of 171 tissue samples were investigated. These comprised 66 benign and 24 malignant thyroid neoplasms, 21 somatotroph adenomas, 35 non-functioning pituitary adenomas, 2 corticotroph adenomas, 1 malignant prolactinoma, and 22 normal pituitary tissue samples. RESULTS: No mutations of PKA Calpha were identified using either allele-specific oligonucleotide hybridisation or single strand conformation polymorphism analysis. CONCLUSIONS: It appears that PKA Calpha mutations at the codons investigated do not represent an oncogenetic mechanism in the development of thyroid and pituitary neoplasms.