  We observe the electron spin resonance of conduction electrons in boron doped
(6400 ppm) superconducting diamond (Tc =3.8 K). We clearly identify the
benchmarks of conduction electron spin resonance (CESR): the nearly temperature
independent ESR signal intensity and its magnitude which is in good agreement
with that expected from the density of states through the Pauli
spin-susceptibility. The temperature dependent CESR linewidth weakly increases
with increasing temperature which can be understood in the framework of the
Elliott-Yafet theory of spin-relaxation. An anomalous and yet unexplained
relation is observed between the g-factor, CESR linewidth, and the resistivity
using the empirical Elliott-Yafet relation.
