The fine structures of the agranulocytes (plasmacytoid cells) with clear roughsurfaced endoplasmic reticulum in the peripheral blood of the clinically normal dogs were studied under an electron microscope. The results thus obtained were summarized as follows. 1) The general figures of the cells were round or oval; however, they had many small rod-or horn-like pseudopodic projections from the contours. 2) The nuclei of the cells had several nuclear indentations or sharp incisions; therefore,

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... generally looked irregular in shape. 3) The presence of poorly to moderately developed rough-surfaced endoplasmic reticulum, a large amount of free ribosomes and well-developed Golgi complex were the characteristics of the cytoplasm of the cells. 4) Judging from the frequency of their appearance, it was proposed that the cells of this type ought to be thought of as one of the usual cellular constituents of the canine peripheral blood.