Ten male Holstein calves were used to examine the effect of milk replacer and solid feed (concentrate and timothy hay) on plasma concentrations of antidiuretic hormone (ADH) and plasma osmolality in suckling calves. One group of 5 calves (500S) received 500g/d of milk replacer and was allowed free access to solid feed for 2wk from 1wk of age. Another group (200 N) was offered 200g/d of milk replacer without solid feed during this period. During wk 2 of the experiment, urine volume decreased but fecal water excretion and apparent water retention (difference between water intake and water excreted into urine and feces) increased in the Group 500S compared with the Group 200N. Plasma ADH concentrations and urine osmolality were higher in the Group 500S than in the Group 200N. Conversely, plasma osmolality did not differ between groups, suggesting an increase in extracellular fluid volume in the Group 500S.