Possible forms of contrast to be expected in field-ion micrographs from specimens containing perfect dislocation loops and dislocation dipoles are discussed in terms of an extension of the type of contrast seen from single isolated dislocations. These predictions are related to the actual contrast seen in field-ion micrographs of these defects. Further, the occurrence of these defects is correlated with the history of the specimens. The paper shows that while the amount of new information that can be obtained on dislocations in general by field-ion microscopy is strictly limited, the technique has distinct utility in studies of small dislocation loops.