Analysis and purfication of structural proteins of intracisternal A particles produced in adenovirus-induced tumor were described. SDS-PAGE of purified intracisternal A particles demonstrated its major structural components, K92, K70 and K55, and minor components, K43 and K37. Two dimensional gel electrophoresis indicated a pI of K70 and K55 at 6.5 and 6.3, respectively, in the presence of sodium dodecyl sulfate. Purification of the main band, K70, in SDS-PAGE using reversed phase-HPLC was difficult in the standard acidic condition, but could be achieved in the neuttral condition. Although purificatin of K70 is generally difficult because of its hydrophobicity, the method shown here will be useful for furthey study of structural proteins of intracisternal A particles.