This study aimed to investigate the neutrophil-lymphocyte ratio (NLR), lymphocyte-monocyte ratio (LMR), and serum iron (Fe) levels, which are hematological criteria, in calves with diarrhea, and to determine their relations with each other. The study material consisted of a total of 171 Brown Swiss, Simmental, and their crossbred female and male calves, aged 0-10 days. The study consisted of eight groups: control group (Group-1, n=15), E. coli group (Group-2, n=32), Coronavirus group (Group-3, n=27), Rotavirus group (Group-4, n=32), Giardia spp. group (Group-5, n=14), Cryptosporidium spp. group (Group-6, n=15), Rota-Coronavirus group (Group-7, n=21), and E. coli- Rotavirus group (Group-8, n=15). The total leukocyte count, neutrophil count, NLR, and Fe levels were found to be significantly different in the diarrhea groups compared to the control group. The NLR values of the E. coli group were higher than the other diarrhea groups and the control group, but the lymphocyte, monocyte, and Fe values were lower. It was concluded that the inflammatory level was higher in the E. coli-induced diarrhea group compared to the other diarrhea groups, and NLR, LMR, and Fe levels yielded significant values in determining the inflammatory status in diarrhoeic calves.