The development of an ultra-miniature optical pressure sensor is proposed for NHLBI's research topics 1. Heart and Vascular Diseases, Biosensors. The sensor is smaller than any of the available pressure transducers, so it can be inserted into blood vessels (arteries, veins, or heart chamber) with an angioplasty guidewire which has a diameter of only 0.4 mm. The sensor can measure blood pressures in the range of O to 300 mmHg with both diastolic and systolic blood pressures. The sensor will operate over time periods of up to a few days without periodical re-calibration. Its pressure readings will be independent of temperature changes in the range of 30 to 50 degrees Celsius. In addition to its functional properties, the sensor has to be disposable and therefore be available at a reasonable cost for clinical use The primary commercial application of this device will be for angioplasty treatment. Because of its small size, the sensor can be used for infants. 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. PROPOSED COMMERCIAL APPLICATION: The device can be used at major hospitals and clinics as an accurate blood pressure measuring device by being inserted into blood vessels (arteries, veins, or heart chamber) with an angioplasty guidewire. Because of its small size, the sensor can also be used to monitor critically ill infants and small children.