The intraosseous pressure (IOP) of the patella was recorded in 12 immature dogs. The mean value of IOP at 90° flexion position of the knee was 12.5±4.7mmHg. The effects of the femoral vascular occulusion and intravenous infusion of adrenaline or noradrenaline on IOP were found to be the same as that of the other reports about the long bones. Application of dopamine slightly increased the IOP, though significant elevation of the systemic blood pressure was observed. During extension or flexion of the knee joint the IOP also increased. Especially, in full flexion this rose to about 1.5 times that in 90° flexion position. With the rise of intraarticular pressure (IAP) of the knee joint the IOP of the patella increesed continuously. But the changes of the IAP during extension or flexion of the knee hardly corresponded to those of the patellar IOP. The morphological condition of the infrapatellar fat pad was observed to be shifting with the motion of the knee, radiographically. Then, it was suggested that not only the elevation of the IAP of the knee but also the compression of the infrapatellar fat pad evoked the rise of the IOP of the patella with the knee movement as a result of venous obstruction.