The biological exploration of the anaphylactoid reaction is based on tryptase and plasma histamine determinations. As this reaction may be considered as a particular case of the acute inflammatory reaction, we have compared, on 25 subjects having presented a drug induces anaphylactoid reaction grade 1 to 3 the plasma level of tryptase, histamine and interleukin 6 (IL6) at 30 and 90 min. On a population of patients having presented an increase of plasma histamine and/or tryptase (n = 14), we have shown that the concentrations of tryptase, histamine and IL6 respectively plateaued (63.9 +/- 70 micrograms/l et 74 +/- 102 micrograms/l), decreased (82.5 +/- 102 mmole/l et 20.5 +/- 27 mmole/l), or greatly increased (19.5 +/- 25.3 ng/l et 320 +/- 745 ng/l) at 30 and 90 min. Correlation between IL6 and the two parameters was only significant for tryptase at 30 and 90 min. Due to the longer lasting kinetic of IL6 (48 h) as compared to histamine and tryptase, IL6 could have a place in the immediate exploration of the anaphylactoid reactions, these results having to be completed by studies on a longer delay and on groups of well defined clinical reactions.