Rubuta ci gaba don wannan sakin layi - Bayan ƙarshen yaƙin Hirszfeld da matarsa sun koma Warsaw, inda ya kafa cibiyar magani mai suna Ehrlich Institute for Experimental Therapy a Frankfurt. Ba da daɗewa ba ya zama mataimakin darektan kuma shugaban kimiyya na Cibiyar Kula da Lafiyar Jama'a a Warsaw kuma, a 1924, farfesa a can. A cikin 1931 an nada shi babban farfesa a Jami'ar Warsaw kuma ya yi aiki a cikin kwamitocin duniya da yawa. Bayan mamayar Poland
Hirszfeld ya kori shi daga Cibiyar Kula da Lafiyar Jama'a a matsayin "wanda ba Aryan ba" amma, ta hanyar kare abokansa, ya sami damar yin ƙarin aikin kimiyya a gida har zuwa Fabrairun 1941; duk da haka, kusan ba zai yiwu a buga shi ba.