The classical experiment of phototropic response as reported by Boysen-Jensen and Nielsen (1926), which supports the Cholodny-Went theory, was repeated in detail. In the original experiment, etiolated oat (Avena sativa L. cv. Victory) coleoptiles with mica inserted into their tip only showed a positive response when the mica was placed parallel toward the light source and not if it was inserted perpendicularly. On the contrary, we found a positive response irrespective of whether the mica was inserted parallel or perpendicularly to the light source. Damage owing to rude splitting severely reduced the response upon perpendicular insertion. These results invalidate the Boysen-Jensen and Nielsen's experiment as a support of the Cholodny-Went theory and lend support to the Bruinsma-Hasegawa theory ascribing phototropism to the local light-induced accumulation of growth inhibitors against a background of even auxin distribution, the diffusion of auxin being unaffected.