In the present study we quantified the contractile protein troponin-T at the cellular and subcellular level in chick embryo cardiomyocytes to investigate the modulation of cardiac development by catecholamines. We analyzed the effects of these drugs on cultures of chick cardiomyocytes obtained from Hamburger and Hamilton's (HH) stage 21, HH stage 29 and HH stage 40 embryos; cardiomyocytes are considered to be mature at HH stage 40. We analyzed the modifications these drugs induced in the transcription of the gene for chick cardiac troponin-T. Sodium dodecyl sulfate-gel electrophoresis and immunobloting showed that cytoplasmic and cytoskeletal concentrations of troponin-T are dependent on the stage of embryonic development analyzed, and on the type of catecholamine added to the culture. The most significant finding was the increase in troponin-T mRNA in the chick heart at HH stage 40, accompanied by an increase in the increase in the expression of this protein in the cytoskeletal compartment after treatment with norepinephrine. At HH stage 21, norepinephrine induced less marked changes in the accumulation of troponin-T in comparison with untreated cardiomyocytes.