The subject of the reproductive toxicity of various forms of radiation can be anxiety provoking to the public on two accounts, since reproductive failure engenders an unusual level of guilt and anger in the affected families, and radiation effects are misunderstood and feared by the public. Reproductive problems include an array of genetic and acquired diseases affecting parents and their offspring. Many of these problems are associated with the risk of being induced by preconception and/or postconception exposures to environmental agents. For the various forms of radiation, namely, ionizing radiation, ultrasound, low-frequency electromagnetic fields (EMF), and microwaves, the potential for producing reproductive effects varies considerably with the form of "radiation" and, of course, the dose. Whether the exposure occurs preconceptionally or postconceptionally is another major consideration. In evaluating the actual reproductive risks, we rely on accurate dosimetry and information obtained in epidemiological studies and animal studies. Epidemiological studies must demonstrate consistency of the reproductive finding, and animal studies should be designed to add to the findings of the epidemiological studies. Most importantly, the conclusions must not contradict the basic principles of teratology, genetics, and reproductive biology, and they should be biologically plausible. But frequently important basic science principles are ignored in the evaluation process. Yet developmental basic science principles can be instrumental in refuting or supporting the concern about possible risks. Although there is some overlap with regard to the preconception and intrauterine effects of ionizing radiation, there are significant differences. Preconception effects are mainly stochastic effects, while intrauterine effects are mainly deterministic effects. The stochastic genetic risks are lower than the deterministic risks at equivalent exposures. Thus, it is frequently difficult to demonstrate the occurrence of stochastic effects in populations that have received low preconception exposures to ionizing radiation. The reproductive effects from preconception and intrauterine exposures to electromagnetic fields (low-frequency EMF, video display terminals, microwaves) and ultrasound represent much different problems, since the main effects of microwaves and ultrasound occur because of their hyperthermic effects at high exposures. Low-frequency EMF does not have the capacity to produce hyperthermia, and none of these forms of nonionizing radiation has the specificity to damage the DNA comparable to the specificity of ionizing radiation. Not only do they not have targeted mutagenic effects at the usual exposures that populations receive, they are not cytotoxic at these exposure levels as well. From the viewpoint of biological plausibility, these other forms of radiation are much less likely to have the potential for producing reproductive toxicity at the usual population exposures.