Heptaprenyl pyrophosphate synthetase from Bacillus subtilis was dissociated into two essential components, none of which had catalytic activity alone. The enzyme activity was restored when the two components were combined with each other. Both fractions, designated components I and II in the order of their elution from DEAE-Sephadex, appeared to be proteins of M r 30 000. Component I was much more stable than component II which was easily destroyed by relatively mild heat treatment. Neither was inter-changeable with any of the essential components of hexaprenyl pyrophosphate synthetase of Micrococcus luteus B-P 26.
