1. Observations made on groups of light and dark skinned individuals indicate that the percentage of dark skinned people who can be recognized as immune by their reaction to vaccination is considerably lower than in the case of people with a lesser skin pigmentation.
2. It is suggested that the reading of "immune reaction" is influenced considerably by the intensity of skin pigment found in the individual.
3. It would appear that while the usefulness of immune reaction readings in light-skinned peope is very great, its value is limited when applied to those with dark skins.