A multi-part construction toy incorporating rod and connector elements, as well as block elements, modified in a way to accommodate the building of hybrid structures utilizing both types of building components. Specialized adapter blocks are provided with openings for receiving special adapter rods. A connector element may be attached in the usual manner to an adapter rod projecting from a block element. For existing rod and connector construction toy sets, the adapter blocks are specially dimensioned to enable multiple attachment points to be established such that complex hybrid structures can be formed. For the large existing base of block type sets, the invention provides a specially dimensioned rod and connector set, compatible with existing toy construction blocks, such that the complex hybrid structures described above can also be executed utilizing existing block elements of standard dimensions.