We have studied the field at which superconductivity nucleates in grain-aligned samples of Y1Ba2Cu3O7-δ very close to the transition temperature Tc. For the field parallel to the c axis and for temperatures within 2 K of Tc, the nucleation field is found to vary as (1-T/Tc)1/2. The data suggest that superconductivity localized near twin boundaries may exist at temperatures close to Tc. .A
