Abstract:The 10 nm diameter filement network in the Chlamydomonas pyrenoid was investigated using selective extraction and diethylene glycol distearate embedding-free electron microscopy. The pyrenoid was cross reacted with animal keratin-antibody using electron microscopic immunogold labeling. Indirect immunofluorescence observation showed the same result. These suggest that a keratin-like intermediate filament network does exist in the Chlam ydomonas pyrenoid.