The article discusses the possible relationships between intestinal microbiota and the therapeutic efficacy of 5-aminosalicylic acid (5-ASA) in inflammatory bowel diseases. Intestinal microbiota may be involved in 5-ASA enzymatic biotransformation, but the metabolism of drugs by the intestinal microbiota has been studied in less detail, and little is known about the relationships between anti-inflammatory efficacy of 5-ASA with bacterial viability, quantity and activity. It remains unclear whether 5-ASA affects the microbiota depending on the different segments of gastrointestinal tract. Drugs and diet can both improve and worsen the composition of the intestinal microbiota. However, it is not known whether drugs affect the intestinal microbiota regardless of diet. Further research is needed to answer these questions.