Japanese quail (Coturnix c. japonica) were fed 0, 2, 4, 8, 16, and 32 p.p.m. Hg as mercuric chloride (HgCl2) from the time of hatching up to the age of 1 year. None of the birds manifested any gross signs of mercury poisoning. Food consumption, growth rate, and weight maintenance were unaffected. Initial oviposition tended to occur at a younger age as dietary mercuric chloride increased, e.g., the median age at which egg laying began among hens fed 32 p.p.m. Hg was 6 days younger than for controls. The average rate of egg production was positively related to the concentration of mercuric chloride with the most pronounced differences between treatments occurring among young (