2014 We consider a gas of atomic hydrogen which is supposed to be stable against molecular recombination and whose internal variables (electronic and nuclear spins) are described by a given density matrix 03C1SI. Since each atom consists of a pair of fermions (one proton and one electron) which is not indissociable due to the possibility of spin exchange collisions, their bosonic behaviour is not obvious a priori. Our aim is to discuss to what extent the pressure of such a gas is actually the pressure of a gas of bosons, our calculation being restricted to the quantum-mechanical second virial coefficient (second order correction in density to the pressure of a dilute gas). We find that this coefficient is the sum of several terms, due either to pure statistics (particle-density effects in the absence of interactions) or to the combined effects of interaction and quantum statistics (role of Vg and Vu potentials). All these terms depend explicitly on the average over 03C1SI of some spin operators. The pure quantum statistical contribution, which is dominant at very low temperature, is related to the exchange of two atoms as a whole (protons and electrons exchanged at the same time), which accounts for its bosonic behaviour. On the other hand, the interaction effects give rise to contributions associated with the exchange of one kind of particle only (protons or electrons) related to the spin exchange collisions, in addition to contributions arising from the exchange of whole atoms. J. Physique 43 (1982) 1199-1211 1 AOUT 1982, 1