Disease states which are abnormal conditions that negatively affects the structure or function of parts or all of an organism usually lead to moderate or extensive tissue damage depending on the time of onset and severity of the disease. Such tissue damages are usually associated with the release of enzymes (specific to the diseased organ or tissue) into circulation which results in an increase in activity of such enzymes in body fluids. The measurement of these changes in enzymatic activity is usually employed as an important clinical assessment tool for detecting, diagnosing, screening and monitoring diseases and pathological processes. Some of the enzymes used in diagnosis include transaminases (in liver diseases), creatine kinase (in myocardial infarction), amylase (in pancreatitis), acid phosphatase (in malignant diseases), and alkaline phosphatase (in bone diseases). Some other enzymes are used as diagnostic reagents in detecting the presence of compounds of clinical importance. These include glucose oxidase (for detecting the presence of glucose), urate oxidase (for testing the presence of uric acid) and cholesterol oxidase (for testing the presence of cholesterol) in diabetes, kidney stones and arteriosclerosis respectively. Various body fluids also contain proteins other than enzymes that are of diagnostic importance especially the plasma proteins. The plasma proteins are broadly divided into two namely; albumin and globulin. The globulins include gamma-globulins, beta-globulins, alpha-1 globulins and alpha-2 globulin. Many physiological and/or disease conditions produce changes in these individual plasma protein concentrations, and measurements of these changes can provide diagnostic information. Some of such enzymes and proteins of diagnostic importance are discussed in this review.