Forty-two calves (mean 10 d of age) that spontaneously contracted diarrhea were used to test the therapeutic value of an oral rehydration solution with or without whole milk. Therapy began on the first feeding after a fecal score was > 2 (five-point scale). Amounts (percentages of BW daily) of milk and oral rehydration solution on d 1 and 2, 3 and 4, 5 and 6, and 7 for treatments 1, 2, and 3 were 1) 0 and 10, 5 and 5, 7.5 and 2.5, 10 and 0% (in two feedings); 2) 2.5 and 10, 5 and 7.5, 7.5 and 5, 10 and 0% (in two feedings); 3) 10 and 10, 10 and 5, 10 and 2.5, 10 and 0% (in three feedings). Oral rehydration solution was fed 15 min after milk. Fecal score, rectal temperature, packed cell volume of whole blood, concentrations of glucose and electrolytes in serum, and strong ion difference of serum were unaffected by treatments. Calves given treatment 3 gained BW throughout the experiment, whereas those given treatments 1 and 2 lost BW during the first 3 d of therapy. Fecal cultures indicated that 70% of calves were infected with Cryptosporidium on d 1 of therapy. No mortality occurred. Whole milk and oral rehydration solution fed to calves did not adversely affect calves or prolong or worsen diarrhea but promoted gain of BW.