Disodium cromoglycate (DSCG) was assessed in controlled experiments as to its effect on human IgE-mediated histamine release from peritoneal rat mast cells in vitro and on the immediate wheal and flare response to antigen, anti-IgE and histamine in 10 atopic individuals. In all 10 atopic individuals DSCG effected no inhibition of the wheal and flare skin reactions caused by 3 antigens, anti-IgE or histamine. The percentage of histamine released was significantly increased by DSCG in the in vitro experiments. As little as 100 μM DSCG induced a threefold increase. The highest increase (fivefold) was effected by, 1,00 μM DSCG. This is in contrast to the inhibitory effect of DSCG on homologous IgE antibody mediated histamine release from rat mast cells.