Haematological and biochemical changes that occurred during the acute stage of infection of newly born lambs infected with Sarcocystis fusiformis and Sarcocystis cameli were presented. Experimental studies had been conducted on nine labs, three-three-months old, divided into 3 groups. The first was left as non-infected control. Each lamb of the second and third groups was inoculated orally with 50,000 S.fusiformis and 50,000 S.cameli sporocysts respectively. Total red blood cells (RBCs), haemoglobin (1-1b), packed cell volume (PCV) and white blood cells count (WBCs), mean corpuscular volume (MCV), mean corpuscular haemoglobin concentration (MCHC), mean corpuscular haemoglobin (MCH), as well as, serum total protein (TP) and its fractions, serum glutamic oxaloacetic transaminase (GOT), creatine phosphokinase (CPK) and lactic dehydrogenase (LDH) were determined weekly for eight weeks. A significant decrease (P<0.05) in RBCs, Hb and PCV started at 3rd week post-inoculation (Pal) in lambs infected with S.fusiformis and at 4th or 5th week P.I. in lambs infected with S.cameli. Also, a significant increase (P<0.05) in WBCs was recorded in 1st - 2nd week P.I.Albumin and A/G ratio decreased, and globulin increased significantly (P<0.05) during the period of 3rd or 4th week to 8th week as week as well as a significant increase (p < 0.05) in GOT from 4th and 3rd week I.P. lambs infected with S.fusiformis and S.cameli respectively. A significant increase (P<0.05) in CPK and LDH was recorded in both infected groups during the interval from 3rd or 4th week to 5th or 6th week P.I.