Abstract.We perform Monte Carlo simulations of the hard-sphere lattice gas on the body-centred cubic lattice with nearest neighbour exclusion. We get the critical exponents, β/ν = 0.311(8) and γ/ν = 2.38(2), where β, γ, and ν are the critical exponents of the staggered density, the staggered compressibility, and the correlation length, respectively. The values of the hard-sphere lattice gas on the simple cubic lattice agree with them but those of the threedimensional Ising model do not. This supports that the hard-sphere lattice gas does not fall into the Ising universality class in three dimensions.In this letter we study the hard-sphere lattice gas whose atoms interact with infinite repulsion of nearest neighbour pairs. The grand partition function iswhere z is an activity and Z V (N) is the number of configurations in which there are N atoms in the lattice of V sites. There are many studies on: the square lattice [1,2,3,4,5,6,7,8,9,10,11,12,13], the triangular lattice [3,6,9,10,14,15,16], the honeycomb lattice [17], the simple cubic lattice [1,3,9,14,18,19], the body-centred cubic lattice [3,9,14,20], and the face-centred cubic lattice [3]. On the simple cubic lattice the author has estimated the critical exponents, β/ν = 0.313(9) and γ/ν = 2.37(2), where β, γ, and ν are the critical exponents of the staggered density, the staggered compressibility, and the correlation length, respectively [18]. The corresponding values of the Ising model are β/ν = 0.518(7) and γ/ν = 1.9828(57) [21]. It does not seem that the hard-sphere lattice gas falls into the Ising universality class in three dimensions. The purpose of this letter is to obtain another piece of evidence of that. We estimate the critical exponents of the hard-sphere lattice gas on the body-centred cubic lattice.We carry out Monte Carlo simulations [22,23] of the hard-sphere lattice gas (1) on the body-centred cubic lattice of V sites, where V = 2×L×L×L (L = 2 × n, n = 2, 3, . . . , 30), under fully periodic boundary conditions [11,18]. We measure the staggered density,and the staggered compressibility,where R = 2 (N A − N B )/V and N A (N B ) is the number of the atoms in the A (B)-sublattice. Each run is divided into ten or twelve blocks. · · · is an expectation in a block and · · · is one over blocks. All the simulations are done at the critical activity, z c = 0.7223, [20] over 12 × 10 5 Monte Carlo steps per site (MCS/site) or 10 × 10 5 MCS/site after discarding 5 × 10 4 MCS/site to attain equilibrium. We have checked that simulations from the ground state configuration (The atoms occupy all the sites of one sublattice and the other 1 is vacant.) and no atom one gave consistent results. The pseudorandom numbers are generated by the Tausworthe method [24,25].We estimate a critical exponent and an amplitude by using the finite-size scaling [26,27,28] Figure 2 shows the size dependence of χ †′ at z = z c . The solid line indicates 0.037L 2.38 . The values of the critical exponents are consistent with those of the hardsphere lattice gas on the simple cubic...