Deviations from ideal parallel packing in;a unidirectional fibre-reinforced composite affect its resistance to splitting. In order to relate, quantitatively, the failure processes to such misorientation, it is necessary to characterize the departure from ideality and to measure the resistance to failure. Experimental observations are presented relating to : (i) a tendency for the carbon fibres in a tow to group into bundles that deviate somewhat from being parallel with each other, and (ii) the fracture toughness for the splitting of several imperfectly aligned composites. Statistical representations are offered for quantifying or modelling the degree of misalignment.