The effects of specimen type (precracked tension or bend) on the relationship between the J-integral and the crack tip opening displacement (COD) and on crack initiation values of J and COD were investigated. The material used was a mild steel. COD was measured by infiltrating the crack with a catalytically hardening silicone rubber. The J-integral was measured both by the compliance technique and using analytical formulae. No significant effect of specimen type was noted. Measurements of J from the analytical formulae used agreed well with compliance measurements. Simultaneous J and COD values were also measured on a low alloy steel. The results indicate that the J/G/COD relationships are material dependent, possibly being controlled by the material's work-hardening rate.