A scanning method is described for measuring the uptake of a labeled compound and the subsequent distribution of this compound or its conversion products over a Sagittaria leaf. The measurement can be repeated several times after the leaf has been extracted with alcohol/aceton, solutions of proteolytic enzymes, dilute acids etc., giving exact data for the distribution of various groups of substances over the length of the leaf. The usefulness of this method is illustrated by some experiments on the uptake and translocation of amino acids in light and in darkness. The results obtained so far indicate a polar, non-specific translocation process, in which the metabolic role of the translocated amino acid seems of minor importance.