The authors biochemically analyzed the nonamyloidotic light chain deposits, the first studied in this way, from a patient with systemic kappa light chain deposition disease (LCDD). The light chain deposits from myocardium were extracted in 6 M guanidine-HCl under reducing conditions, partially purified by column chromatography, and analyzed by immunoblotting and amino-terminal sequencing. The extracted material contained four main bands reactive with anti-kappa antibody: intact kappa light chain (MW, 28 kd), under reducing conditions, and 3 fragments (MW, 20, 16, and 15 kd). As revealed by the aminoterminal sequencing performed on three of the four bands, the intact light chain molecule and two fragments belong to the kappa I subgroup. Thus, similar to light chain amyloid (AL), the deposits in LCDD are derived from both intact light chain and fragments. Unlike in AL, amyloid P component was not detected in the deposits of this patient or those examined previously. The differences demonstrated thus far between AL and LCDD are the lack of fibrils and amyloid P component in LCDD, suggesting that local tissue factors may be responsible for different processing of the light chain deposits in LCDD.