A cDNA encoding the human fast-twitch skeletal muscle isoform of troponin I (TnIfast) has been sequenced. This cDNA is 701 base pairs in length, and encodes a protein of 182 amino acids. TnIfast is the last of the three known human TnI isoforms to be sequenced. Comparison of the deduced human TnIfast protein sequence with a variety of troponin I isoforms from other species has revealed a high degree of cross-species sequence conservation between TnIfast proteins.