Serum and urine concentrations of protein, urea, Na and K were monitored between birth and 72 h in neonatal pigs. Serum protein increased (p < 0.05) 37 mg/ml after suckling, while urinary protein temporarily increased (p < 0.05) to 14.7 ± 0.98 mg/ml by 12 h but declined (p < 0.05) to birth values by 72 h. Urinary urea levels tripled (p < 0.05) by 12 h and remained elevated. The ratio of urea in the urine to that in the serum ranged from 17 to 29. Serum Na concentrations were stable (141–146 mEq/l) during the 72 h, and urinary Na levels were low (9–44 mEq/l) and decreased (p < 0.05) by 72 h. Serum K fluctuated and was highest (p < 0.05) at birth (6.4 ± 0.26 mEq/l) and lowest by 72 h (4.4 ± 0.26 mEq/l). Levels of K excreted in the urine were high (20.0–7.6 mEq/l) compared to blood levels. Colostral concentrations of Na were low (81–73 ± 3.8 mEq/l) while K levels were high (24.3–28.8 ± 1.39 mEq/l) compared to piglet serum levels.