We describe a newly developed enzyme immunoassay (EIA) for the determi
nation of 6-sulphatoxy-melatonin (aMT6s) in human urine, using a aMT6s
-bovine serum albumin-horseradish peroxidase (aMT6s-BSA-HRP) conjugate
as the enzyme label, The assay incorporates a highly specific antibod
y raised in rabbits. The EIA has a sensitivity of 2 pg/well (40 pg/ml)
with intraassay coefficients of variation of 2.3-6.1% in the range of
the assay. The material with the highest level of cross-reactivity wa
s N-acetyl serotonin sulphate, with a relative potency of 0.000078%. O
ne hundred thirty-four urine samples from children and adults at diffe
rent time points were assayed and the results compared with those from
an established radioimmunoassay (RIA) and with a newly developed RIA
using the same antibody as the EIA. The correlation coefficient, r; co
mparing the two RIA's was 0.9869, and the regression equation was log
(kit) = 0.9340 log (new) + 0.1213. The correlation coefficient, I; com
paring the EIA with the newly developed RIA, was 0.9686, and regressio
n equation log (new) = 0.9674 log (EIA) + 0.0600. The EIA for the meas
urement of aMT6s in urine represents a new approach in the investigati
on of pineal function.