Urine excretion rates of the collagen crosslinks lysylpyrridinoline and hydroxylysylpyrridinoline. Urine samples were collected twice weekly and the excretion rates of the major collagen-crosslinks (a), (c) hydroxylysylpyrridinoline (HP) and (b), (d) lysylpyrridinoline (LP) were determined as described in Materials and methods. Urinary excretion rates were normalized to creatinine levels to compensate for a possible dilution factor. In Experiment I, two animals with overt clinical arthritis (Mi121, Mi125) show increased production from either (a) HP and/or (b) LP. In Experiment III, the production of (c) HP and (d) LP was less affected by the disease. Only in animals with a high number of joints involved in the disease ( > 10 affected joints) was an increased production of both HP and LP observed. PID, post induction day.