The performance of cements containing secondary main constituents ( SMCs ) and additions is discussed in relation to the relevant British standards. It is proposed that BS EN 197-1: 2000 omits several important requirements in relation to CEM I. This standard lists allowable SMCs, but no justification is given for the maximum allowable proportions of each. An evaluation test for each SMC is required to determine the free water:cement ratio for each cement type. BS EN 206-1: 2000 has restrictive and limited provision for additions, with BS 8500-2 2002 determining the proportion of additions by cement equivalence testing rather than using the "k-value concept". The equivalence testing does not consider the influence of additions on the water demand. k-values according to BS EN 206-1: 2000 are not based on the formal test method nor related to strength. It is concluded that the lower band limits for free water:cement ratio should be such that the appropriate impenetrability level for the given durability class is achieved. Also, that the ratio limits should consider the proportion and type of clinker, SMC and addition, and that the performance of these materials should be evaluated on the basis of in-situ performance. 25 refs.