The developmental changes and correlations of some hormone levels and immune parameters in six spontaneously delivered Holstein calves with a birth weight of 40-50 kg were studied for a postnatal period of 1-15 days after birth. The mean levels of insulin (I), glucagon (Gc), cortisol (C) and growth hormone (GH) before feeding on day 1 were 9.68 +/- 3.27 muu/ml, 685.39 +/- 95.42 pg/ml, 14.27 +/- 5.58 micrograms/dl and 0.85 +/- 0.10 ng/ml respectively. I and GH increased on day 2 and then decreased to a steady level. Gc and C fell fluctuantly within week 1 and remained at a stable level after then. WBC, neutrophil percentage, B-lymphocyte percentage, albumin percentage decreased with day of age in 1st week and lymphocyte percentage, T-lymphocyte percentage, T-G (total globulin) percentage and gamma-G percentage increased with day of age in 1st week and then reached a steady level. The correlations between some hormone levels and immune parameters indicated that C and Gc have significantly negative correlations with gamma-G (%), T-G (%) and T-lymphocyte (%) respectively. WBC is positively correlated to C and Gc significantly. The correlations of I and GH with some immune parameters have no significance.