Experimental spirochaeta infection was done in Fayoumi chickens of different age (3-7 weeks old). It was proved that the young chicks were susceptible to infection. Pathological examination revealed that the spleen was the principle organ mostly affected by spirochaeta followed by liver, kidneys and intestine. Histopa thological examination of the internal organs and lymphoid tissues was performed. Blood haematology showed generally anaemia and leucopenia due to the decrease of heterophils and lymphocytes.