The critical point drying method of preparing samples for scanning electron microscopy is associated with a variable amount of specimen shrinkage. We studied the causes of this phenomenon is isolated mouse hepatocyte nuclei and in human erythrocytes and found that the critical point drying process itself caused most of the shrinkage that we observed (a 25-30% reduction in diameter in both specimens). Glutaraldehyde fixation and ethanol dehydration caused only minimal size reduction, prior to critical point drying. Substitution of an inert (ethylene glycol-ethylene glycol monethyl ether) dehydration technique did not alter the final result. Previous studies in our laboratory using high resolution SEM and correlative transmission microscopy of isolated nuclei have demonstrated that the shrinkage represents a miniaturization of the organelles in which all structural components retain their usual relationships.