The development of a fiber optics pressure catheter is proposed for NHLBI Subject 56.D, 1991. The optical pressure sensor using elasto-optic materials would be the smallest in diameter (less invasive) among currently available electronic and optical pressure catheters. It is inserted into blood vessels (arteries, veins or heart chamber) and is capable of measuring blood pressures (O to 300 mmHg) with a very high accuracy (better than 3 mmHg). The sensor is bio-compatible and causes no medical problems. The sensor is also stable over long time periods (72 hrs.) and for temperature changes (30 to 50 degrees centigrade). The manufacturing cost of the sensor head would be very inexpensive (less than $lO) so that it can be disposable. The sensor will help monitor heart conditions after open heart surgery. Because of its small size, the sensor can be used for infants. The primary commercial application of this device will be in cardiology. It can also be used to monitor fluid pressures in the human brain after surgery. The Phase I effort demonstrated the feasibility of the proposed approach. Prototype development will be carried out in Phase II.