1. The technic used to determine the average volume per cell of leukocytes from patients with leukemia has been described.
2. The distribution of the average volumes of leukocytes from 15 patients with granulocytic leukemia, based on 52 determinations, has a median value of 450 cu. µ and a mean of 460 cu. µ. 2. The 95 per cent range for this distribution is 340 to 570 cu. µ.
3. Sufficient data are not presently available to determine the Shape of the distribution for the volume of monocytes, but the average value for the leukocytes from 8 patients with monocytic leukemia is 470 cu. µ and the range is 360 to 580 cu. µ.
4. The average volumes of leukocytes from 27 patients with lymphocytic leukemia, based on 74 determinations, have a Poisson-like distribution with a median value of 230 cu. µ and a mean of 250 cu. µ. Ninety-five per cent of the values in this distribution fall in the range of 130 to 410 cu. µ.
5. Although leukocyte volumes from both granulocytic and lymphocytic leukemias follow Poisson-like distributions, the central values of these distributions are significantly different. However, there is an overlap of the distributions with approximately a 15 per cent chance that average lymphocytic volumes will fall into the range of the small granulocytic volumes.
6. For many purposes it may be assumed that two billion cells of the granulocytic or monocytic series or four billion cells of the lymphocytic series equal 1 ml.