Abstract: A water-soluble carboxypolysaccharide-magnetic iron oxide complex of small particle diameter composed of a water-soluble carboxypolysaccharide and a magnetic iron oxide having a core diameter ranging from about 2 to about 7 nm, wherein the total diameter ranges from about 10 to about 50 nm, the ratio of the total diameter to the core diameter is about 15 or less, and the T.sub.2 -relaxivity ranges from about 10 to about 150 (mM.sec).sup.-1. Said complex has low toxicity and small side effects and is useful in the fields of medical treatment, biology and engineering as an iron-supplementing agent, an X-ray contrast medium, an MRI contrast medium, a reagent for blood flow rate measurement, a carrier for drug administration, etc.

Abstract: The invention relates to nanocrystalline magnetic particles consisting of gnetic iron oxide core of Fe.sub.3 O.sub.4, gamma-Fe.sub.2 O.sub.3 or mixtures thereof and an envelope chemisorbed to said core, the method for preparation of these particles as well as the use thereof in medical diagnostics and/or therapy. The magnetic particles, according to the invention, are characterized by composition of the coating material of natural or synthetic glycosaminoglycans and/or their derivatives with molecular weights of 500 Da to 250,000 Da, if necessary, covalently cross-linked with appropriate cross-linking agents and/or modified by specific additives.