Filter paper has been tested as a medium for the collection of blood samples for the subsequent elution and analysis of phenylalanine, tyrosine, glucose, and urea nitrogen. The use of paper did not measurably alter the precision of the above methods. The paper punch as a means of quantification has been compared with the more commonly used technic of volumetric measurement. The precision obtained with punched spots was found to be similar to that found with measured spots for the above four procedures and for weighed samples. The hematocrit value was found to have an influence on the volume of blood contained in a punched spot. Differences in spreading through filter paper between 100 individual blood samples tested did not seem to be responsible for a variance in excess of that introduced by the analytic procedures themselves.