A nuclear matrix was obtained from isolated nuclei of bovine lymphocyte by digestion with DNase I and subsequent extractions with 0.4 M and 2.0 M NaCl. 91.1 % of the nuclear protein, 99.5 % of the DNA and 83.1 % of the RNA were removed from isolated nuclei by these treatments. with the following nuclease digestion, almost all residual DNA and RNA was removed leaving the nuclear protein matrix.Ultrastructural analysis of the nuclear matrix revealed a spherical structure containing a peripheral lamina, an internal fibrogranular network and residual nucleoli.Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the nuclear matrix demonstrated three major polypeptides of 68, 000, 53, 000 and 43, 000 dalton as well as more than 50 minor polypeptides of various molecular weight classes. The 68, 000 dalton polypeptide corresponds to lamin B, one of three predominant polypeptide components of rat liver nuclear matrix. However, polypeptides corresponding to lamin A and C were not detectable in the bovine lymphocyte nuclear matrix. Hiroshi Nakayasu