Mean levels of MPA in blood taken 90 days after injection were not significantly different between women who had received a single injection of DepoPrevera and those who had received eight injections at 90-day intervals. There was a wide variation in plasma MPA concentration in the two groups of women. In women who had received 31 to 45 injections of CycloProvera, plasma levels of MPA 28 days after injection were significantly higher than those of women who had received a single injection. The levels were also higher than those found in women 90 days after injection of DepoProvera. The results suggest that the dose of MPA in CycloProvera could be reduced.