A noninvasive antibody test was used to identify male fragile X patients in special education schools, on the basis of the lack of FMRP in hair roots. We studied 300 males with mental retardation of unknown cause attending special schools. Patients were divided into two groups, based on the scores according to a fragile X check list (Group 1 less than or equal to 9 points and Group 2 greater than or equal to 10 points). Group 2 consists of 51 males and only 5 males in this group showed no FMRP expression in hair roots within the abnormal range (91%), Fragile X diagnosis in these cases was confirmed by DNA analysis. None of the males scoring more than 10 on the check list was diagnosed positive for the fragile X syndrome using DNA analysis. With our antibody test on hair roots we did not detect a fragile X patient in Group 1, The FMRP antibody test on hair roots is suitable in a screening program for the fragile X syndrome among mentally retarded males attending special education schools. (C) 2000 Wiley-Liss.