||Kondo insulator materials such as CeRhAs, CeRhSb, YbB12, Ce3Bi4Pt3, and SmB6, are 3d, 4f and 5f intermetallic compounds. At high temperatures they behave like metals but a gap d in the conduction band opens at the Fermi energy as the temperature is reduced. It has been proposed that the formation of the low-temperature gap is a consequence of the hybridization between the conduction band and the f-electron levels. If this is true, Kondo metal physics should be recovered when the gap is closed at high magnetic fields. We report here specific heat results of Ce-3 Bi4Pt3 in DC and pulsed magnetic fields up to 60 T. We see evidence for the reduction of the gap in 18 T and a rapid increase of the Sommerfeld coefficient C-H/T\(T -->0) in 30 T > H > 40 T. Numerical results and the analysis of the data with the Coqblin-Schrieffer model prove a field-induced Kondo insulator-to-Kondo metal crossover. (C) 2001 Elsevier Science B.V. All rights reserved.