1. A new, quick, sensitive and specific assay for the quantitative determination of proline is presented together with its automatization. The use of glacial acetic acid-formaldehyde as the solvent for ninhydrin lends a series of advantages to the reaction. 2. A serial automated procedure for the simultaneous detection of proline, hydroxyproline and hydroxylysine in one single sample is pesented. The advantage of the triple assay lies in the use of one single sample instead of three previously aliquoted fractions in three individual automated assays. The triple assay is as specific, reproducible and sensitive as the individual assays. 3. A quick, manual assay for hydroxylysine is presented. This method represents a further simplifiction of previous ones by the same author and adds the advantage of rapidity to their sensitivity and specificity.