1. The biological half-life of radiophosphorus in egg-laying Habrobracon females is four to five days.2. A majority of the P32 lost, about 60%, is by way of deposited eggs. This is based upon excretory studies using a newly devised technique, and upon comparisons of laying and non-laying wasps. Direct evidence of the radioactivity of the eggs is also presented.3. The radioactivity of eggs rises to a peak reached the second day after feeding. Subsequent to the third day, it drops sharply to a relatively low plateau.4. The variability in radioactivity from egg to egg is greatest in the first day. It may prove to be less each succeeding day.5. During the first day almost 90% of the ingested radioactive material is abdominal due to the location of the crop. From the second to the fourth day about 65% of the radioactivity in the female is abdominal. Subsequently abdominal radioactivity approaches 50% of the total. Of these proportions less than one-third may be gonadal.6. Although it is an important factor in ...