Gd3+-ions can be released from GBCAs after in vivo application and polysaccharides like glycosaminoglycans are candidates for binding of released Gd3+-ions by acting as competing chelators. We showed that the chelation of Gd3+-ions to polysaccharides cause an increase of R1 due to the high relaxivity of such complexes. However, at high GAG/Gd3+ ratios and in cell experiments, we observed a decrease of R1 after the chelation of Gd3+. Our results demonstrate the importance of more in vivo-like setups for the investigation of gadolinium transchelation processes to prevent an underestimation of the amount of deposited gadolinium in biological tissues.