The ecology of the tuna, its large size, and extensive migratory habits precludes a direct study of much of its life history. Its spawning habits have, consequently, been largely approached by such indirect methods as collecting juvenile stages and planktonic eggs, size at its first sexual maturity, and year classes based on the commercial catch, etc. The present study is an at¬tempt to add to our knowledge of the spawning behavior of Philippine tuna through the statistical analysis of growth of the ova in the ovary by measuring their increasing diameters. This method was developed by Thompson (1915) and success¬fully employed by such investigators as Clark (1925, 1929, 1934); De Jong (1940); Hickling and Rutemberg cited by De Jong (1940) ; and Mane (1929, 1934). The following com¬mercially important species of Philippine tuna were considered in the present study: Neothunnus macropterus, Katsuwonus pelamis, and Euthynnus yaito.