Gingival crevicular fluid (GCF) is an important source for the assessment of periodontal and peri-implant disease activity and response to periodontal therapy. GCF contains cellular components such as epithelium, bacteria, leukocytes, erythrocytes, viruses and their by-products, electrolytes, bacterial metabolic products, host and bacterial enzymes, and enzyme inhibitors such as acid phosphatase, alkaline phosphatase, cytokines, and immunoglobulins. In addition, it is also found that drugs taken systemically pass into the GCF.