Background: Prolonged and intense physical exercise causes multiple significant changes in the body. These changes can lead to health disorders and deterioration of physical fitness. Objective: Marathon runners require medical attention and the performance of laboratory assays. Hence we planned to study blood lactate and haematological parameters in young healthy subjects before and after the marathon Methods: The study group comprises 19 healthy medical students aged between 20-25 years who are amateur nonprofessional runners. Blood lactate level, Anthropometric parameters and haematological parameters were estimated before and after the half marathon, using standard assay procedures. Results: We found a significant increase (P__ampersandsignlt; 0.001) in blood lactate level after the marathon as compared to before the marathon. We also confirmed leukocytosis after the half marathon and decreased percentages of lymphocytes and eosinophils; while the percentage of monocytes, haemoglobin concentration, HCT, RBC, MCH, MCV, and MCVC after the marathon remained unchanged. Conclusion: Marathon running is a prolonged and intense physical effort that leads to several changes in the organism, as demonstrated by the results of haematological parameters and blood lactate analysis. The growing popularity of long-distance running, especially among amateurs, indicates the importance of biochemical investigations during such activity.