The therapeutic and anti-inflammatory properties of sodium alginate and one of its components, β-d-mannuronic acid, were tested in various experimental models. On the basis of its chemical structure, β-d-mannuronic acid had been conceived as an anti-inflammatory drug. β-d-Mannuronic acid is a constituent of alginate but is not available commercially; hence, polymannuronate was obtained from an epimerase (AlgG) negative mutant of Pseudomonas sp. and the monomer was isolated by acid hydrolysis. The oral and intraperitoneal administration of alginate gels in experimental models of ulcerative colitis and glomerulonephritis as well as the oral administration and intraperitoneal injections of β-d-mannuronic acid in different models of rheumatoid arthritis, multiple sclerosis, glomerulonephritis, and nephrotic syndrome showed that alginate as well as β-d-mannuronic acid are able to exhibit their therapeutic efficacy in inflammatory diseases. Recent experimental evidence has revealed that β-d-mannuronic acid represents a novel nonsteroidal anti-inflammatory drug with a low molecular weight and which provides a new therapeutic option in attenuation of inflammatory reactions and autoimmune diseases.