'Arthroscopic volume' and resorption of normal saline was measured in 35 young males during routine arthroscopic examination. The average mean volume of the knee joint cavity was 103.4 ml and this volume was observed to correlate with the midpatellar circumference of the knee and the height of the patients. Mean resorption of normal saline was 4.1 ml/min, this resorption correlating with the volume of the joint cavity. No correlation with the underlying disease of the knee was observed.