A method of utilizing the 
chymotrypsin level of an individual as a measure of the success of 
secretin, other neuropeptides, and peptides or 
digestive enzyme administration to such individuals, and in particular, as a prognosticative of potential 
secretin, other neuropeptides, peptides, and 
digestive enzyme administration for persons having ADD, ADHD, 
Autism and other PDD related disorders. In one aspect, a method for determining the 
efficacy of 
secretin, other neuropeptides, peptides, or digestive enzymes for the treatment of an individual diagnosed with a 
pervasive developmental disorder (PDD) comprises obtaining a sample of 
feces from an individual, determining a quantitative level of 
chymotrypsin present in the sample, and correlating the quantitative level of 
chymotrypsin determined to be present in the sample with the PDD to determine the 
efficacy of treating the individual with secretin, other neuropeptides, peptides, or 
digestive enzyme administration. In another aspect, a therapeutic method for treating an individual diagnosed with a PDD 
pervasive developmental disorder comprises determining the 
efficacy of secretin, other neuropeptides, peptides, and digestive 
enzyme administration for the treatment of the 
individual based on a measure of the individual's chymotrypsin level, and administering secretin, other neuropeptides, peptides, or digestive enzymes to the 
individual based on the determination of the measure of the individual's chymotrypsin level.