A comparison of metaphase arresting agents and tritiated thymidine. Autoradiography in measurement of the rate of entry of cells into mitosis in the crypts of Lieberkühn of the rat.

Three methods of estimating cell production rate were used: the rate of accumulation of metaphases blocked by Colcemid, or by vinblastine, and the rate of increase of labelled nuclei after administration of tritiated thymidine. These rates were determined for three sites in the small intestine by counts made on whole micro‐dissected crypts, fixed at various times after the administration of the agents. Within the limits of error of the methods, the cell production rate per crypt was the same when measured by each method (35/hr), and showed a slight fall from the proximal to the distal end of the small intestine (36/hr to 33/hr). the advantages and limitations of each method are discussed.