Objectives In this study, we presented 2 cases and evaluated the evid ence for symptomatic hypocalcemia after treatment with magnesium sulfate alone or combine d with use of nifedipine. Study design Case reports, such as the one that follow s, and literature review were used. A 25-year-old gravida presented at 33 week sgestation with advanced preterm labor. She received magnesium sulfate followe d by nifedipine and experienced bilateral hand contractures 12 hours after disco ntinuation of magnesium sulfate. Total serum calcium was 5.4 mg/dL. A 35-year- old gravida presented at 26 weeksgestation with ruptured membranes and receive d magnesium sulfate until it was discontinued prematurely because of pulmonary e dema. Twenty hours later she experienced bilateral hand contractures; total seru m calcium was 5.9 mg/dL. Symptoms for both patients resolved with calcium glucon ate therapy. Results Hypocalcemia is a well-recognized complication of magnesiu m sulfate infusion. These are the fifth and sixth symptomatic case reports, as i dentified by Medline Search. Our first case is the only report in which the subs equent use of nifedipine may have been a factor. Little has been reported on the possible toxicity associated with the combined or sequential use of magnesium s ulfate and nifedipine. Conclusion Marked hypocalcemia is clearly associated with magnesium sulfate infusion, is likely dose related, and may appear after discon tinuation of magnesium sulfate therapy. Moreover, while the evidence for synergi stic toxicity of magnesium sulfate and nifedipine is sparse, caution is advised when these agents are used together. Objectives In this study, we presented 2 cases and evaluated the evid ence for symptomatic hypocalcemia after treatment with magnesium sulfate alone or combine d with use of nifedipine. Study design Case reports, such as the one that follow, and literature review were used. A 25-year-old gravida presented at 33 weeks s’gestation with advanced preterm labor. She received magnesium sulfate followe d by nifedipine and experienced bilateral hand contractures 12 hours after disco ntinuation of magnesium sulfate. Total serum calcium was 5.4 mg / dL. A 35-year-old gravida presented at 26 weeks’gestation with ruptured membranes and receive d magnesium sulfate until it was discontinued prematurely because of pulmonary e dema. Twenty hours later she experienced bilateral hand contractures; total seru m calcium was 5.9 mg / dL . Symptoms for both patients resolved with calcium glucontete therapy. Results Hypocalcemia is a well-recognized complication of magnesiu m sulfate infusion. These are the the fifth and sixth symptomatic case reports, as i dentified by Medline Search. as first devised only by the Medline Search. of magnesium s ulfate and nifedipine. Conclusion Marked hypocalcemia is clearly associated with magnesium sulfate infusion. is likely dose related, and may appear after discon tinuation of magnesium sulfate therapy. Moreover, while the evidence for synergi stic toxicity of magnesium sulfate and nifedipine is sparse caution is advised when these agents are used together.