Available, but tentative and incomplete biological criteria of use in assessing human hazards from nuclear explosives were presented along with the source of data from which they were derived. The criteria were related to effects parameters employing free-field, some "geometric," and translational scaling to the end that areas at potential risk from nuclear detonations ranging in yield from one kt to 100 Mt could be estimated. The problem areas involved and many of the uncertainties due to lack of both physical and biological data as well as to the fact that the conditions of exposure represent a major factor in determining the environmental variations that challenge man and hence in controlling the incidence of casualities as well as survival were noted and briefly discussed. The utility of the range-yield-effects relationships set forth was emphasized as was the need for a continued collaborative understanding biological response on the one hand and basic effects phenomentology on the other.