Regularly arranged cytoplasmic microtubules are present in blood platelet fixed in liver sinusoids during aldehyde perfusion of the animal. This finding in addition to other recent reports on the cytoplasmic microtubule suggests that these organelles might be found in all cytoplasm if the ultrastructure is preserved adequately. Note: Subsequent to the submission of this article a description of filaments and microtubules in spread platelets by Bessis and Breton-Gorius18 appeared. The greater number of filaments in their illustrations suggests a breakdown of some of the microtubules to the smaller filaments.11 These authors speculate on the possibility of a contractile function for microtubules.