Critical field measurements were performed on a cylindrical rod of single-crystal Mo3Re. The isothermal, magnetic transitions were extremely sharp and reversible, indicating that the specimen was approaching nearly ideal properties. The principal data are: Tc=9.80°K, H0=530 gauss, (dHcdT)T=Tc=-114 gauss/deg. The deviation from parabolic behavior D(t) indicated a positive maximum value of 0.065. On the basis of this present work, we suggest a possible correlation between the thermodynamic critical field and the "filamentary" critical field noted for the high-field superconducting materials.