ELA, Volume 16, pp. 435-443, December 2007, abstract. Block Distance Matrices R. Balaji and R.B. Bapat In this paper, block distance matrices are introduced. Suppose F is a square block matrix in which each block is a symmetric matrix of some given order. If F is positive semidefinite, the block distance matrix D is defined as a matrix whose (i,j)-block is given by D_{ij}=F_{ii}+F_{jj}-2F_{ij}. When each block in F is 1x1 (i.e., a real number), D is a usual Euclidean distance matrix. Many interesting properties of Euclidean distance matrices to block distance matrices are extended in this paper. Finally, distance matrices of trees with matrix weights are investigated.