Stress relaxation measurements were made on wall material from internodal cells of Nitella. The observations were made in the temperature range 0 to 50° C for the interval 1 to 300 sec and the apparatus used for this purpose is described. The time-temperature correspondence of the data and its relevance to the ultrastructure and molecular organization of the cell wall is discussed. Adjustments during relaxation occur in the ‘amorphous’ materials linking the microfibrils and not in the microfibrils themselves. The indications are that these materials, designated as ‘amorphous’ through the lack of an X-ray diagram, may nevertheless be highly ordered. Values of tensile moduli deduced from these measurements agree with those of other workers using direct methods.