He specialized in iatrochemistry and iatrogenesis,[1] and was the first to develop a syringe to inject dye into human reproductive organs so that he could understand their structure and function.

[3][4] There his co-students were Jan Swammerdam, Niels Stensen, Ole Borch and Frederik Ruysch, cooperating with professor Franciscus Sylvius, Johannes van Horne and Lucas Schacht.

As a correspondent of the Royal Society in London, De Graaf recommended (at the end of April) Henry Oldenburg that attention should be paid to autodidact Antonie van Leeuwenhoek and his work on the improvement of the microscope.

[6][7] It has been speculated that he may have committed suicide, but it is more likely it was malaria, typhoid fever or dysentery as in other Dutch cities;[8][5] the disease persisted throughout the year, peaking in July and August.

De Graaf's position in the history of reproduction is unique, summarising the work of anatomists before his time, but unable to benefit from the advances about to be made by microscopy, although he reported its use by Antonie van Leeuwenhoek in 1673.

De Graaf may have been the first to understand the reproductive function of the fallopian tube, described the hydrosalpinx, linking its development to female infertility.

De Graaf's contemporary Jan Swammerdam confronted him after his publication of DeMulierum Organis Generatione Inservientibu and accused him of taking credit of discoveries he and Johannes van Horne had made earlier regarding the importance of the ovary and its eggs.