The present invention relates to a method for risk-stratifying subjects suffering from B-precursor acute lymphoblastic leukemia (ALL), wherein said subjects are intended for a therapy comprising administration of a CD3 binding domain. Risk-stratification is based on the determination of the amount blast cells in a bone marrow sample from said subject, and/or on the determination of the number of blast cells per 1 μl in a CSF sample from said subject. According to the category into which subjects are risk-stratified, said subjects can be appropriately treated, while their risk of a potential adverse neurological reaction can be reduced or even excluded.