Results of screening tests for the detection of inborn errors of metabolism in 1,117 consecutive patients are reported in this work; patients came for a second consultation to the Departamento de Genética, Centro Médico de Occidente, IMSS. Simple qualitative test were made that revealed the presence of abnormal metabolites (amino-acids, sugars, organic acids and mucopolysaccharides) in urine and blood as well as identification tests for variant proteins. Results were positive in 138 patients and test for confirmation and/or specificity were made in all patients; in 35 the following diagnosis and incidence were established: classic galactosemia, 2; glucose-6-phosphate dehydrogenase deficiency, 20; essential pentosuria, 1; hyperphenylalaninemia, 5; blue diaper syndrome, 1; cistinuria 1, and type 1 mucopolysaccharidosis, 5.