- 350 - second degree in age was used when there was a significant departure from linearity. The criteria vibratory sense, hand grip, light extinction time, hand tally count, and body potassium showed significant sex differences, and therefore were scaled for each sex (zero to 100%). An attempt to correlate a combined ''physiological'age score with chronological age was done by obtaining a weighted average score for combined criteria for each age group (see Table I). The absolute value of the correlation coefficients were used as the weighting factor. This has intuitive appeal, since the influence on the final combined score of any particular ageing criterion is proportional to the absolute value of its correlation with age. Results The results of these tests are presented graphically in figs. 1-14 and in Table I. The mean values for each decade starting at age 20 are plotted at the midpoint of that decade for exposed and unexposed groups separately and combined, along with the standard errors of the means. The curve or straight line (whichever best represents the particular data) is drawn and its equation presented, The coefficient of correlation with age and significance is also presented, Most of the criteria show good correlation with ageing. It is apparent that most of the criteria show the least change with age in the younger age groups, from 20-40 years of age, particularly for systolic blood pressure, hearing, visual acuity, neuromuscular functions, and skin retraction. Above about 40 years of age the criteria show the greatest change. With a few criteria, changes in the older age group tend to level off or be less steep (accommodation, visual acuity, skin looseness, cholesterol). In Table I age and radiation dependence of these criteria are presented, The criteria are arranged in descending order of correlation with ageing as shown by the correlation coefficients. In those criteria in which Sex differences were apparent, the r value for the two sexes were averaged to determine the overall correlation with ageing, Though there were isolated significant differences between the exposed and unexposed age groups for some criteria, no meaningful pattern emerged. The table shows that the correlation with radiation effects, comparing exposed and unexposed groups, is not significant at the 5% level for any of the criteria, The overall 7% increase in ageing effects in the exposed group is not significant (p = 0. 27). In fig. 15 the composite weighted biological or physiological age scores are graphically plotted against chronological age (means per decade), Combined mean values for exposed and unexposed groups are also presented with standard errors of the means. The overall correlation of the biological age scores with chronological age is very good (see Table 1), The biological