Whakaotihia te rerenga e whai ake nei: I muri i te mutunga o te pakanga ka hoki a Hirszfeld me tana wahine ki Warsaw, i reira i whakatuhia ai e ia he whare serum i hangaia i muri i te Ehrlich Institute for Experimental Therapy i Frankfurt. Kaore i roa ka noho ia hei kaiwhakahaere tuarua me te upoko pūtaiao o te State Hygiene Institute i Warsaw, a, i te tau 1924, he kaiwhakaako i reira. I te tau 1931 i whakaingoatia ia hei kaiwhakaako tuuturu i te Whare Wananga o Warsaw a he maha nga poari o te ao. I muri i te
I te wā o te noho a te ope Tiamana ki Polani, ka tukuna a Hirszfeld hei "kore-Arian" mai i te Whare Hauora, engari, na te tiaki o nga hoa, i kaha ki te mahi rangahau i te kainga tae noa ki te Hui-tanguru 1941; heoi, he mea uaua ki a ia te whakaputa.