Antisense and sense (control) cRNA probes of TGF-beta1 and IGF-I, labeled with digoxigenin, were used to localize the growth factor transcripts by in situ hybridization. mRNA levels (densitometric ratio of growth factor/glyceraldehyde-3-phosphate dehydrogenase) of TGF-beta1 and IGF-I in HCM (0.75+/-0.05 and 0.85+/-0.15, respectively; mean+/-1 SEM) were significantly (P<.01 for all groups) elevated in comparison with non-HCM myocardium (AS: 0.38+/-0.07, 0.29+/-0.06; SA: 0.32+/-0.04, 0.18+/-0.05; TM: 0.25+/-0.03, 0.15+/-0.03). mRNA levels of TGF-beta1 and IGF-I in the hypertrophic AS myocardium were greater (P=.02, P=.05) than those in the explanted myocardium (TM).