Heterophil to lymphocyte ratios during perinatal and neonatal stages in chickens.

1. Heterophils (H) and lymphocytes (L) were measured in embryos that had pipped into the air cell and through the shell, and in chicks from 0-d-old to 8 d of age. 2. Numbers of lymphocytes in the perinatal stages were very low with H:L ratios greater than 5.0. 3. Posthatching H:L ratios decreased in a quadratic manner from 1.76 at hatch to 0.39 on day 8.