The amino acid composition and halogen content of the bath sponge, Spongia officinalis obliqua (D. & M.), collected in the Gulf of Mexico, was studied to determine the nature of the halogenated amino acids present. The sponge was found to contain 1.06% tyrosine, 0.38% iodine, and 0.80% bromine. It is believed that the major halogenated amino acids are the mono- (3-) and di- (3, 5-) bromo- and iodotyrosines.