The present study was carried out to represent a field problem in squabs of domestic pigeons (columba livia) at Ismailia Province. Squabs were grossly examined and showed typical lesions including yellowish caseous, fibronecrotic patches in mouth due to infection with T. gallinae. Forty squabs were collected and tested individually for the presence of Trichomonas gallinae (T. gallinae). Squabs were divided into equal four groups, the 1st was un-infected control group, the 2nd was T. gallinae infected untreated group, the 3rd and the 4th groups were T. gallinae infected and treated with metronidazole. The obtained results showed that the mortality (%) were 0, 50, 20 and 30 % in 1st, 2nd, 3rd and 4th group, respectively. Body weight was significantly reduced in all groups, although the drugs improved the weight reduction as compared to pre-treatment. Organs' weights were significantly increased after treatment as compared with the control group. Serum biochemical analysis revealed significant elevation in total protein, globulins; β- globulin and γ- globulin but albumin , α-globulin levels and A/G ratio were significantly reduced in infected squabs and increased in treated groups. Serum urea, creatinine and uric acid levels were increased, while, Serum glucose , cholesterol Na, K, Ca, P, Mg and serum iron as well as plasma ChE activity were decreased in both treated and infected groups. Serum AST, ALT, LD, γ -GGT, CK, AP activities were significantly increased in infected groups, Destructive changes in buccal cavity, hyperemia in blood vessels, necrotic changes in the liver with leucocytic infiltration and demylination of brain with preivascular oedema were observed.