AbstractFour sites (a, b, c, d) are considered of differing seismicity. The calculations, for two different buildings on each site, consisted of:1.The total monetary cost as a function of the design seismic coefficient c.2.The marginal cost of a saved life, ΔD/ΔL, also depending on c.3.The ratios between the design seismic coefficients in the various sites, cd/ca, cd/cb, cd/cc, that lead to the same marginal cost ΔD/ΔL in all sites.The marginal cost ΔD/ΔL turns out to be highly sensitive to uncertainties, but the other ratios are scarcely influenced by the uncertainties met in analysing the problem. This would suggest the adoption of a rationalized principle for comparing the levels of severity in the Codes for sites with differing degrees of seismicity.If a criterion for evaluating indirect cost due to damage or collapse is fixed for each building and each site the values of c corresponding to minimum monetary cost are not strongly influenced by the said uncertainties. This would make it possible to look into the problem of the minimum levels of severity in the Codes. Of course, this assumes that the levels of severity should always be higher than those corresponding to the minimum monetary