1. Clearance and micropuncture studies were performed in four groups of acutely thyropara-thyroidectomized animals to study the effects of alkalosis and acidosis on the renal handling of magnesium.
2. Our results indicate that chronic metabolic acidosis reduces, whereas acute metabolic alkalosis enhances, magnesium reabsorption.
3. The site within the nephron where absorption of magnesium increases or decreases during acid-base disturbances was beyond the late proximal tubule.
4. Tubular fluid bicarbonate was also measured in these experiments, and the results indicated that magnesium reabsorption in the distal tubule correlated to bicarbonate delivery. However, whether this was a direct or an indirect effect of bicarbonate on magnesium transport could not be delineated.