Abstract: A building block, of generally the same overall shape as a concrete or cinder block, is provided and includes upper and lower recesses and projections which interlock the blocks in tiers of blocks for compact storage and shipment and which enable the blocks of adjacent courses of blocks to be interlocked with each other during construction of a wall. In addition, the blocks include reinforcing members embedded therein for transferring vertical loads through vertically stacked courses of blocks and some forms of reinforcing enable cementitious material poured into the cavities of the block to be reinforced. One form of reinforcing is tubular and includes bell and spigot ends which may be sealingly engaged with each other and used to allow heating or cooling fluids to flow through the blocks.