Though individual asteroids or planetoids orbiting between Mars and Jupiter may be small, they are bound to exert influences in the horoscope. In light of this conclusion, they must also exert the same type of cross chart influence in the area of relationships. With this premise, Emma Belle Donath wrote Asteroids in Synastry.

Using her vast store of mythological as well as astrological lore, she tells the myths of the four major asteroids, as well as giving keyword lists and rulerships for each. In the body of the book she gives delineation of the asteroids using the most accepted forms of synastry (person A's planets in person B's chart and vice versa). In addition, she gives some of the major aspect configurations between charts, and takes a brief look at composite charts and contact cosmograms. Several example charts are used to illustrate asteroid use in this manner. This is the definitive text for using asteroids in synastry.