Parallel to the determination of astrometric parameters for some 100,000 stars, the HIPPARCOS data may also be used to study the light deflection produced by the sun. Cowling (1983 thesis) has calculated the light deflection observable by HIPPARCOS for a general space-time metric, and we have included his list of fifteen metric coefficients as “global” parameters in simulated HIPPARCOS reductions. The estimated covariance matrices show that only 7–9 linear combinations of the Cowling parameters may be determined with some accuracy (~10−10). The value for the standard GR light deflection may be determined if the thermal effects on the satellite are small, but not to better than about 0.5%.