The aim of this study was to investigate methylene blue reduction time of ruminal fluid in some forestomach diseases of cattle. Ten cattle with simple indigestion (BI), 15 cattle with traumatic retuculoperitonitis (RPT), 15 cattle with chronic rumen acidosis (KRA) and 10 healthy cattle (Control Group) were used in the study. Methylene blue reduction time was performed in rumen fluid samples of the cattle. Methylene blue reduction time of the rumen fluid samples was determined as 3,5 min, 12,4 min, 10,53 min and 2,53 min in the Control Group and in the cattle with BI, RPT and KRA, respectively. Methylene blue reduction time of ruminal fluid in the cattle with BI and RPT was significantly increased compared to the controls. Methylene blue reduction time of ruminal fluid in the cattle with KRA was decreased compared the controls but it was not significant statistically. In conclusion, methylene blue reduction time which is an indicator of anaerobic fermentation of rumen fluid might be a practical test in the diagnosis of commonly seen forestomach diseases of cattle.