A rapid colorimetric test for the determination of thebaine in dried, extracted Papaver bracteatum is described. The method is based on the development of an orange color formed by the nitroso color reaction for phenols. The absorption peak is near 450 nm. The linear range response is from 0 to 1.0 mg of thebaine. The reproducibility of the method is quite good, making it useful for process evaluation and in a selection program for the cultivation of P. bracteatum for optimum thebaine content.