Conditions for a transition from the insulator (I) to metal (M) state in the electron system of highly oriented pyrolytic graphite (HOPG) have been studied by means of magnetotransport measurements in a broad temperature range (0.3–150 K). In magnetic fields below a certain critical value (B < B c ≈ 0.05 T), HOPG exhibits the classical magnetoresistance, while for B > B c, the temperature dependence of the resistance is determined by the state (insulator versus metal) of the electron system. The M-I transition in HOPG, by analogy with that in heterostructures with two-dimensional electron gas, obeys the power law T c ∞ (B − B c) k (k = 0.25) and is related to the spin-orbit interaction of electron waves.