Holographic interferometry has been used to determine the differential stress concentration at the tip of a craze as a function of over‐all strain. The differential stress concentration factor &dgr;K&sgr;yyis unity at low strains. Upon further strain increase, &dgr;K&sgr;yyincreases, passing through two maxima before it finally decreases again to approximately a value of unity before fracture. In addition, the differential craze opening displacements of, and stress increments borne by, various regions along the craze have been determined as a function of strain. It is found that the craze opens unevenly, with the base of the craze opening at lower applied stresses than the craze tip. As a result, the differential stress concentration in the craze at a point well behind the craze tip can be greater than that at the craze tip. The strain dependence of &dgr;K&sgr;yyis in qualitative agreement with that expected, given the nonlinear stress‐strain curve of similar crazes measured by Kambour and Kopp. A detailed explanation of the stress concentration and the uneven craze opening requires consideration of the structural differences between craze fibers in the base and tip of the craze as well as the possibility of structure differences along individual fibers in the craze.