Adaptive cardiac hypertrophy in the rat has been characterized as pathological or physiological reflecting the nature of the inciting stimulus. These two adaptations are distinguished by alterations in contractility and in the myosin ATPase composition of the affected muscle. We investigated the relative amounts of the mRNAs encoding cardiac sarcoplasmic reticular calcium ATPase (SERCA2), cardiac and skeletal troponin I (TnI), atrial natriuretic factor (ANF). and myosin light chain 1 (MLCI) in the hearts of rats that had been subjected to either conditioning by swimming (Sw), to renovascular hypertension (H) or to the combined stimulus (H-Sw) for 6 weeks. Compared to control animals, the mRNA levels for SERCA2 and cardiac TnI were slightly increased with Sw and moderately depressed with H. H-Sw animals showed a trend towards normalized mRNA levels for both genes. ANF mRNA levels were slightly elevated with Sw and markedly elevated with both H and H-Sw. MLC1 mRNA levels did not change with either or both stimuli. These data confirm that these two types of adaptive hypertrophy can be distinguished at the level of gene expression and suggest that the mechanical alterations seen in adaptive hypertrophy reflect a spectrum of pre-translational alterations which are not limited to changes in myosin heavy chain gene expression.