Organophosphorous pesticides (OPs) are suspected of altering reproductive 
function by reducing brain acetylcholinesterase activity and monoamine levels, 
thus impairing hypothalamic and/or pituitary endocrine functions and gonadal 
processes. Our objective was to evaluate in a longitudinal study the association 
between OP exposure and serum levels of pituitary and sex hormones. Urinary OP 
metabolite levels were measured by gas-liquid chromatography, and serum 
pituitary and sex hormone levels by enzymatic immunoassay and radioimmunoassay 
in 64 men. A total of 147 urine and blood samples were analyzed for each 
parameter. More than 80% of the participants had at least one OP metabolite in 
their urine samples. The most frequent metabolite found was diethylthiophosphate 
(DETP; 55%), followed by diethylphosphate (DEP; 46%), dimethylthiophosphate 
(DMTP; 32%), and dimethyldithiophosphate (DMDTP; 31%). However, the metabolites 
detected at higher concentrations were DMTP, DEP, DMDTP, and dimethylphosphate. 
There was a high proportion of individuals with follicle-stimulating hormone 
(FSH) concentrations outside the range of normality (48%). The average FSH serum 
levels were higher during the heavy pesticide spraying season. However, a 
multivariate analysis of data collected in all periods showed that serum FSH 
levels were negatively associated with urinary concentrations of both DMTP and 
DMDTP, whereas luteinizing hormone (LH) was negatively associated with DMTP. We 
observed no significant associations between estradiol or testosterone serum 
levels with OP metabolites. The hormonal disruption in agricultural workers 
presented here, together with results from experimental animal studies, suggests 
that OP exposure disrupts the hypothalamic-pituitary endocrine function and also 
indicates that FSH and LH are the hormones most affected.