Hi Alan, You are right about Higman's lower bound. A simple modification of Higman's argument gives that there are at least p^{2*n*n*(n-9)/27} groups with order p^n, class 2 and exponent p. So asymptotically there are also p^{2(n^3)/27} groups with order p^n, class 2 and exponent p. All the best, Mike (Newman)