Adrenergic receptors (ARs) are involved in regulating saliva secretion and composition in salivary glands. Nine AR subtypes, including three alpha1-ARs (alpha1a-, alpha1b- and alpha1d-ARs), three alpha2-ARs (alpha2A-, alpha2B- and alpha2C-ARs) and three beta-ARs (beta1,beta2- and beta3-ARs), have been identified through molecular cloning. The five subtype genes, alpha1a-, alpha1b-, alpha2A-, beta1-, and beta2-ARs, were expressed in rat submandibular glands. In contrast, the other four subtype mRNAs, alpha1d-, alpha2B-, alpha2C- and beta3-ARs, were not detected by reverse transcription-polymerase chain reaction (RT-PCR). The steady-state mRNA expression for the five AR subtypes in rat submandibular glands was measured by quantitative competitive RT-PCR using synthetic DNA as internal standard at different stages of postnatal development. The relative rank order of AR subtype mRNA expression was alpha1a>beta2>beta1>alpha2A>alpha1b at all stages except that beta1- and alpha2A-subtypes were reversed at 2 weeks of age. The gene expression of alpha1a-AR subtype relative to total AR was low at 2 weeks of age and increased and reached a maximum at 6 weeks of age, whereas those patterns of alpha2A-, beta1- and beta2-AR subtypes were similar to each other and their gene expressions were high at 2 weeks of age and then decreased. On the other hand, the gene expression of alpha1b-AR subtype did not change over the different stages in relation to that of a housekeeping gene, glyceraldehyde 3-phosphate dehydrogenase, and to total AR. Although rat submandibular glands contain the five AR subtype mRNAs, distinct subtype-specific expression is evident.