Fifty-nine women completed a randomized, double-blind placebo-controlled study of pyridoxine hydrochloride (vitamin B6) for the treatment of nausea and vomiting of pregnancy. Thirty-one patients received vitamin B6, 25-mg tablets orally every 8 hours for 72 hours, and 28 patients received placebo in the same regimen. Patients were categorized according to the presence of vomiting: severe nausea (score greater than 7) or mild to moderate nausea (score of 7 or less). The severity of nausea (as graded on a visual analogue scale of 1-10 cm) and the number of patients with vomiting over a 72-hour period were used to evaluate response to therapy. Twelve of 31 patients in the vitamin B6 group had a pre-treatment nausea score greater than 7 (severe) (mean 8.2 ± 0.8), as did ten of 28 patients in the placebo group (mean 8.7 ± 0.9) (not significant). Following therapy, there was a significant difference in the mean “difference in nausea” score (ie, baseline — post-therapy nausea) between patients with severe nausea receiving vitamin B6 (mean 4.3 ± 2.1) and placebo (mean 1.8 ± 2.2) (P<.01). In patients with mild to moderate nausea and in the group as a whole, no significant difference between treatment and placebo was observed. Fifteen of 31 vitamin B6-treated patients had vomiting before therapy, compared with ten of 28 in the placebo group (not significant). At the completion of 3 days of therapy, only eight of 31 patients in the vitamin B6 group had any vomiting, compared with 15 of 28 patients in the placebo group (P<.05). The adjusted odds ratio for emesis in the treatment versus placebo groups, stratified by the presence or absence of pre-treatment emesis, was 0.1156 (P<.005). In conclusion, the mean “difference in nausea” score in patients with severe nausea and the total number of patients with vomiting were significantly reduced following vitamin B6 therapy