The aim of this investigation was to determine the metabolism of glyburide (GL) by microsomes prepared from placentas obtained from uncomplicated pregnancies (UP), women with gestational diabetics (GD) on a diabetic diet, and those on a diet and GL. Term placentas were obtained from UP and GD. Crude microsomal fractions were prepared by differential centrifugation and stored at -80 degrees C. The activity of the microsomes in metabolizing glyburide to the trans-4-hydroxycyclohexyl glyburide (THCGL) and cis-3-hydroxycyclohexyl glyburide (CHCGL) was determined and quantified using high-performance liquid chromatography-mass spectrometer (HPLC-MS). The activity of the placental microsomes varied widely between individual placentas in each group. The median values (pmol.mg (-1) P.min (-1)) for the rates of THCGL formation were 0.34, 0.3, and 0.23 for placentas of UP, GD on diet, and GD on GL and a diet, respectively. The median values for CHCGL formation were 0.13 for UP, 0.11 for GD on a diet, and 0.10 (pmol.mg (-1) P.min (-1)) for GD on GL and a diet. A pool of individual microsomal fractions from each group was prepared and its activity revealed the following: greater formation of THCGL in the UP (0.36 +/- 0.10) than GD (0.22 +/- 0.03) ( P = 0.058 for GD on a diet, 0.04 for GD on GL). There was greater formation of CHCGL in UP (0.26 +/- 0.04) than GD (0.12 +/- 0.003) ( P < 0.006). There was no difference in GD on a diet and GD on GL plus diet. We concluded that the apparent differences in the formation of metabolites may be statistically significant, but it is unlikely to be of physiological importance, given the sample size and other experimental factors. Therefore, a more comprehensive investigation is underway.