Leukocytes from ten allergic patients (five allergic to dust-mites and five allergic to pollen) were treated with N-acetyl aspartyl glutamic acid (NAAGA) 4.9%, disodium cromoglycate (DSCG) 2%, lodoxamide (LODO) 1%, and levocabastine (LEVO) 0.5% (concentrations representing the pharmaceutical eyedrop preparations) for 20 minutes. Degranulation was then induced with Complement (rHu5Ca). Histamine was measured in the supernatant with ELISA. LODO and LEVO were inactive in blocking histamine released from human cells, and paradoxical unexpected effects were found with these two agents. They both induced significant histamine release in almost 100% of the samples. DSCG was able to block histamine release in seven patients out of nine (ranging between 5 and 34%). NAAGA was the most active agent on human cells and was able to block basophil degranulation in nine patients out of nine (inhibition ranging between 4 and 66% of total histamine pool).