We report here for the first time the optical visualization of microsomal degranulation induced by a carcinogen (p-dimethylaminoazobenzene), employing analytical ultracentrifugation. Our observations demonstrate that electrophiles of a carcinogen can disrupt ribosome-membrane interaction in rough microsomes by their attacks on nucleophilic components of the reticular membrane-ribosome complex involved in protein synthesis for export from the cytosol. Lack of exported proteins can adversely affect signal transduction across plasma membrane, possibly leading to carcinogenesis.