The application of the histamine liberation test to the diagnosis and follow-up of allergic processes has been pursued by many authors. Since Shore first described a manual fluorimetric technique, efforts have been directed at automating the system and reducing the sample volume. According to the latest contributions by Moneo et al., from 300 to 400 determinations can be carried out in a single work day, and from 40 to 50 determinations with 10 ml of blood. In the present work we present our experienced in updating the technique and the system of preparation of a histamine standard, which we consider of great practical use in the application of this technique routine. Using the standard solution as reference, we calculated total and basal histamine levels in 342 presumed healthy individuals; the mean values were 69.5 ng/ml for total histamine and 8% for basal histamine in males, and 71 ng/ml for total histamine and 6% for basal histamine in females. Age range was from 17 to 57 years, and there were no differences between sexes. The maximum value was 176 ng/ml and the minimum 32 ng/ml. The reaction of O-phthaldialdehyde with histamine is not chemically specific. In the presence of light, aldehydes self-polymerize; moreover, O-phthaldialdehyde can react with other products in addition to histamine. The first problem is avoided by protecting the reagents from light, and the second by using specific absorption and emission filters which do not pick up signals from reaction side products. Nevertheless, at the quantitative level these effects are negligible when compared to other causes which, although not part of the chemical reaction, are also involved in the process (antigen standardization, etc). By means of this technique, from 300 to 400 determinations can be carried out in a single work day, making it possible to use this technique in the daily work routine.