In situ hybridization of cloned cDNA probes to frozen sections of Xenopus laevis stage-42 tadpoles has been used to determine the tissue localization of several mRNAs. Nine out of sixteen probes tested hybridized to most or all tadpole tissues; seven probes exhibited tissue-specific hybridization. The non-tissue-specific sequences hybridized to RNA species that are also present in maternal RNA while the tissue-specific sequences hybridized to embryonic RNA species induced after gastrulation and undetectable in maternal RNA. Tissue-specific hybridization was observed with muscle (five clones), epidermis (one clone), and the nervous system (one clone). All muscle-specific sequences hybridized to somites and lateral plate muscles, but they differed in their hybridization to heart muscle.