Subtypes of alpha(1)-adrenoceptor (alpha(1)-AR) in the cultured myoblast C(2)C(12) cells have been examined using molecular biological identifications. Expression of the two distinct mRNAs that encode proteins of alpha(1A)- and alpha(1B)-AR was studied using reverse transcription combined with polymerase chain reaction (RT-PCR). Results of RT-PCR demonstrated a marked expression of alpha(1A)-AR in the prostate of rats. Samples from the C(2)C(12) cells under the same amount of amplification showed the expression of alpha(1A)-AR at a level slightly lower than that from the prostate of rats. Western blotting analysis using receptor subtype-specific antibody also indicated that the alpha(1A)-AR was expressed in C(2)C(12) cells as well as in prostate of rats. However, although the expression of alpha(1B)-AR was obtained in the spleen of rats, expression of alpha(1B)-AR was undetectable in the C(2)C(12) cells either the results of RT-PCR or the Western blotting analysis. The present study suggests that alpha(1A)-AR is a major subtype of alpha(1)-AR in the C(2)C(12) cell line.