These two abnormalities are reviewed, including results of original anatomical studies on Norway spruce and Douglas fir. Hazel grain and true wavy grain are generally formed by wavelike variations in radial increment in a direction perpendicular and parallel to grain respectively. Anatomical characteristics and general occurrence suggest that hazel grain is endogenous (possibly genetic) and wavy grain due to mechanical disturbance. In hazel-grained spruce and Douglas fir, the mean fiber length was reduced in tangential sectors of reduced increment. Although a normal range of fiber lengths was present in these sectors, the modal fiber length was markedly shorter than normal; the mean fiber length was not significantly different in earlywood and latewood. This reduction in mean fiber length is probably related to the hypertrophied ray parenchyma in these sectors. Because hazel grain does not affect the quality of spruce resonance wood, results suggest that resonance quality is determined by the optimum latewood/annual ring width ratio (1:3). Only true (semiaxial longitudinal) wavy grain is regarded as a wood defect. -- AATA