Complete map of the nematode's neurons. Sulston and Horvitz tracked every non-gonadal cell division that occurred during larval development, and published a complete description of these lineages in 1977.

Using C. elegans to investigate whether there was a genetic program controlling cell death, or apoptosis,  In 1986, Horvitz identified the first "death genes", ced-3 and ced-4. He showed that functional ced-3 and ced-4 genes were a prerequisite for the execution of cell death.

Horvitz and colleagues identified several key components in the molecular pathway of programmed cell death, including: EGL-1, a protein which activates apoptosis by inhibiting CED-9.