Ovary gland cells of Aptenia cordifolia were exposed to 100 micrograms/ml cytochalasin B (cyt B) for 30 or 60 min during the phase of granulocrine polysaccharide secretion. The drug caused a congestion of Golgi vesicles around the dictyosomes, probably resulting from an inhibition of the vesicle migration towards the plasma membrane. The ultrastructural feature of the Golgi apparatus in control and cyt B treated cells was analyzed using stereological methods in order to estimate the mean area of vesicular membrane produced by a single dictyosome during a 30 min period of effective cyt B action. Assuming that the rate of vesicle congestion can be equated with the rate of vesicle production, the 236 dictyosomes found to be present in the non-growing ovary gland cells form 7517 vesicles in total, or approximately 32 vesicles each within a period of 30 min. This corresponds to a membrane turnover rate of 70.4 micrometers/min (this equals approximately 10% of the total plasma membrane area per min), since the mean vesicle surface area was calculated to be 0.281 microns2. The turnover time of a single Golgi cisterna was determinated to be 7.34 min, and the average vesicle life time to be 8.86 min. Discussion focuses upon the way by which the relatively high amount of vesicular membrane material incorporated into the plasmalemma is recycled into the endomembrane system. Since a bulk membrane retrieval in the form of vesicles, as well as a bulk vesicle migration from the ER to the dictyosomes could not be observed, we suggest that a transfer of membrane subunits is involved in the maintenance of membrane equilibrium in the Golgi apparatus.