In this paper we study the sequence (c(i))(0 <= i <= d) for a distance-regular graph. In particular we show that if d >= 2j and cj > 1 then c(2j-1) > c(j) bolds. Using this we give improvements on diameter bounds by A. Hiraki, J.H. Koolen [An improvement of the Ivanov bound, Ann. Comb. 2 (2) (1998) 131-135], and L. Pyber [A bound for the diameter of distance-regular graphs, Combinatorica 19 (4) (1999) 549-553], respectively, by applying this inequality. (c) 2004 Elsevier Ltd. All rights reserved.