Linkage for a schizophrenia susceptibility locus on chromosome 22q12-q13 was initially suggested by independent studies from two groups and confirmed in a combined analysis of data for the microsatellite marker D22S278 in multiply affected schizophrenic families derived from 11 independent research groups worldwide. In addition to these reports of linkage to schizophrenia on chromosome 22, bipolar disorder has also been linked to markers in this chromosomal region. We now report results from an analysis of 223 Palestinian Arab trios from 3 different centers in Israel and Palestine using the allele-wise Extended Transmission Disequilibrium Test for multiallelic markers (ETDT). No evidence for linkage is observed in the entire group nor in any of the three centers (entire group: chi-square = 5.59, P=0.78, df = 9; Afula: chi-square = 6.51, P=0.48, df= 7; Bethleham: chi-square = 14.11, P=0.12, df = 9; Beersheva: chi-square=7.04, P=0.32, df = 6). Additionally, we examined D22S278 in a group of 114 schizophrenic German triads and also failed to observe evidence for linkage (chi-square = 8.13, P=0.42, df = 8df).