Axel, along with microbiologist Saul J. Silverstein and geneticist Michael H. Wigler, discovered a technique of cotransformation via transfection. This process, which allows foreign DNA to be inserted into a host cell to produce certain proteins, is fundamental to recombinant DNA research at pharamceutical and biotech companies. Order of authorship in the original publication: Wigler, ...Silverstein, Axel.

"In their landmark paper published in 1991, Buck and Axel cloned olfactory receptors, showing that they belong to the family of G protein coupled receptors. By analyzing rat DNA, they estimated that there were approximately one thousand different genes for olfactory receptors in the mammalian genome. This research opened the door to the genetic and molecular analysis of the mechanisms of olfaction" (Wikipedia article on Richard Axel, accessed 7-22).
For this and later work showing that each olfactory receptor neuron expresses only one kind of olfactory receptor protein...Axel and Buck received the 2004 Nobel Prize in Physiology or Medicine.