Having established previously the variability of the tensile strength of foundry cokes and the relations between tensile strength and micum indices, a study has been made to determine whether blast-furnace cokes show similar behaviour. Using the diametrical-compression test and applying the Weibull statistical theory of strength to the data, tensile strength parameters of a representative series of blast-furnace cokes were determined and the variability within coke lumps, between individual lumps and between different cokes was ascertained. It was demonstrated that the variability and the range of values of the tensile strength of blast-furnace cokes are similar to those shown by foundry cokes; however in contrast to foundry cokes there is no direct correlation between the tensile strength and the micum index, whether M 40, M 10 or non-standard indices down to M 0.5, nor between the material constants provided by the application of the Weibull statistical theory to the tensile strength data for blast-furnace cokes and any of the micum indices. It was concluded from this that there are significant differences in the breakage processes followed by blast-furnace and foundry cokes, probably attributable to differences within the coke structure of the distribution or type of flaws associated with fracture. Whether the basic cause lay in differences of carbonizing conditions or differences in the types of coal blend used could not be established from the evidence available.