Reef sampling was continued in Galveston, Matagorda and San Antonio Bays to study trends in the oyster (Crassostrea Virginica) population. In Galveston a continued decline in spat and seed oyster stock occurred, with a lesser decline in market oyster stock. Matagorda Bay oyster stocks, which had suffered extensive mortality in 1964, showed only slight recovery. In San Antonio bay, the oyster population in the central bay, which had been decimated by disease in 1964, increased in abundance, but oyster stocks in the lower bay area diminished. Sring and late summer mortalities were common in all areas sampled. Generally, summer mortalities exceeded those in spring. Dermocystidium marinum infections were high in Galveston Bay but low, or negative, in other areas. The presence of ABO (Aransas Bay Organism) was suspected in Matagorda Bay and San Antonio Bay but was not confirmed. In spite of declining oyster stocks, the 1965-66 harvest set a new record of over four million pounds. As in past years, almost all of the harvest came from Galveston Bay.