We study magnetotransport properties of graphite and rhombohedral bismuth samples and found that in both materials applied magnetic field induces the metal-insulator- (MIT) and reentrant insulator-metal-type (IMT) transformations. The corresponding transition boundaries plotted on the magnetic field-temperature (B - T) plane nearly coincide for these semimetals and can be best described by power laws T ∼ (B - Bc)κ, where Bc is a critical field at T = 0 and κ = 0.45 ± 0.05. We show that insulator-metal-insulator (I-M-I) transformations take place in the Landau level quantization regime and illustrate how the IMT in quasi-3D graphite transforms into a cascade of I-M-I transitions, related to the quantum Hall effect in quasi-2D graphite samples. We discuss the possible coupling of superconducting and excitonic correlations with the observed phenomena, as well as signatures of quantum phase transitions associated with the M-I and I-M transformations. © 2006 Elsevier Inc. All rights reserved.