Let N > 1 be an integer, and let C=C 0 (N) … SL 4 (Z) be the subgroup of matrices with bottom row congruent to (0, 0, 0, *) modN. We compute H 5 (C; C) for a range of N and compute the action of some Hecke operators on many of these groups. We relate the classes we find to classes coming from the boundary of the BorelSerre compactification, to Eisenstein series, and to classical holomorphic modular forms of weights 2 and 4. © 2002 Elsevier Science (USA)