[1] He was notable for the first hypothesis regarding cellular processes that cause cancer, and for describing chromatin diminution in nematodes.

[4] Using an optical microscope, Boveri examined the processes involved in the fertilization of the animal egg cell; his favorite research objects were the nematode Parascaris and sea urchins.

Boveri's work with sea urchins showed that it was necessary to have all chromosomes present in order for proper embryonic development to take place.

[7][12] He proposed carcinogenesis was the result of aberrant mitoses and uncontrolled growth caused by radiation, physical or chemical insults or by microscopic pathogens.

[13][14] His assumption was initially rejected by medical professionals; it was only later that researchers such as Thomas Hunt Morgan in 1915 demonstrated that Boveri was correct.