Intra-day changes in the levels of biochemistry parametersA n organism needs energy regularly for maintaining its life and functions. The main energy nutrients include carbohydrates, lipids, and proteins [1]. Fasting and nonfasting statuses are the most interesting issues in the nutritional area [2]. People mostly live in the nonfasting state during a normal 24-h cycle. Therefore, nonfasting metabolic panels may be a confident indicator of average biochemical parameter levels because the fasting state only consists after fasting for at least 8 h [3,4]. At hospital laboratories, biochemical tests are generally performed on samples taken on fasting (preferably) between 08:00 and 10:00 [5]. Due to the increased workload of hospitals since the 2000s, patients have to wait for hours for sample collection even if they arrive at hospitals early in the morn-ing [6]. This situation might cause stress in patients. Due to reasons such as the difficulties of employees in getting permission from their jobs and the fast pace of life, patients visit hospitals to provide their samples for testing in the evening. Additionally, the number of blood samples taken during nonfasting may often be higher than the number of those taken during fasting. In another aspect, it might not be possible for children and infants, who constitute an important part of the population, to stay hungry for many hours. The increased average age of the population also increases the number of patients aged over 70 years and those with chronic diseases. Prolonged fasting may cause health problems in these people. In fact, the body's metabolism is in a state of nonfasting Objectives: People mostly live in the nonfasting state during a normal 24-h cycle. This study aims to compare the levels of 18 biochemical parameters during different hours of the day. Methods: A total of 18 biochemical tests of patients who visited outpatient clinics only once between January 1, 2010, and December 31, 2019, were evaluated at the Hatay Mustafa Kemal University (HMKU) Central Laboratory by using hospital database information. The tests are albumin (Alb), aspartate aminotransaminase (AST), alanine aminotransaminase (ALT), alkaline phosphatase (ALP), amylase, blood urea nitrogen (BUN), calcium (Ca), total cholesterol (TC), creatine kinase (CK), creatinine (Cr), gamma-glutamyltransferase (GGT), glucose, high-density lipoprotein cholesterol (HDL-C), inorganic phosphorus (Pi), iron (Fe), total protein (TP), triglyceride (TG), and lipase. The blood samples of the patient were divided into eight groups according to their collection time as follows: (a)