We report conduction electron spin resonance measurements performed on highly oriented pyrolitic graphite samples between 10 and 300K using S (ν = 4GHz), X (ν = 9.4GHz), and Q (ν = 34.4GHz) microwave bands for the external DC-magnetic field applied parallel (H ∥ c) and perpendicular (H ⊥c ) to the sample hexagonal c-axis. The results obtained in the H ∥ c geometry are interpreted in terms of the presence of an effective internal ferromagnetic-like field, H int eff(T, H), that increases as the temperature decreases and the applied DC-magnetic field increases. We associate the occurrence of the H int eff(T, H) with the field-induced metal-insulator transition in graphite and discuss its origin in the light of relevant theoretical models. © 2002 Elsevier Science B.V. All rights reserved.3201-4413415Xu, S., (1996) Phys. Rev. Lett., 76, p. 483Kopelevich, Y., (1999) Fiz. Tverd. Tela (St. Petersburg), 41, p. 2135Kopelevich, Y., (1999) Phys. Solid State, 41, p. 1959Kopelevich, Y., (2000) J. Low Temp. Phys., 119, p. 691Kempa, H., (2000) Solid State Commun., 115, p. 539Khveshchenko, D.V., (2001) Phys. Rev. Lett., 8720, p. 6401Dresselhaus, M.S., Dresselhaus, G., Sugihara, K., Spain, I.L., Graphite fibers and filaments Springer Series in Material Science, 5, pp. 179-188. , references therein, Springer, BerlinDresselhaus, M.S., (1981) Adv. Phys., 30, p. 139Sercheli, M.S., (2002) Solid State Commun., 121, p. 579Laughlin, R.B., (1998) Phys. Rev. Lett., 80, p. 5188Ferrer, E.J., cond-mat/0101308