SUMMARY Seven mutants which have low activities of vegetative (phosphate-repressible) alkaline phosphatase have been mapped by transduction crosses. These mutations do not affect the production of the alkaline phosphatase associated with sporula- tion. All the evidence available suggests that the activities produced in phosphate- starvation and during sporulation are attributable to the same protein and derive, presumably, from a common structural gene. It thus appears that alkaline phos- phatase has distinct sporulation and vegetative controls and that all the mutations so far examined have been of the regulator type. The position on the chromosome of the structural gene is still in doubt.