To examine the effect of BSA on the cell surface of mast cells, the (45)Ca influx was observed in mast cells from actively sensitized rats and also in cells passively sensitized with IgE-containing serum before or after purification by BSA. The mast cells from actively sensitized rats showed a marked increase in the (45)Ca uptake with stimulation by ovalbumin. The value of (45)Ca uptake by the cells was 1495 ± 104 cpm / 10(5) cells. The uptake of (45)Ca by mast cells passively sensitized before or after separation through BSA was also increased in response to ovalbumin, although the degree of 45Ca uptake by the latter showed marked variation. These results may
suggest that BSA affects mast cell surface when the cells are sensitized after separation by BSA.