That public bureaucrats, like most other people, might pursue their private interests as voters, job applicants and union members is hardly surprising. It is the postulate that bureaucrats' self-interested behavior penetrates their role as public decision-makers that represents a challenge, empirical-theoretically as well as normatively. To assess the assumption that bureaucrats' self-interests affect bureaucrats' decisions in their capacity as officials (the self-interest hypothesis), two main points are made. First, the probability that self-interests are conceived and made operational in different issue areas is considered. Second, it is argued that the explanatory power of bureaucrats' self-interests has to depend on characteristics of the self-interest phenomenon itself, for instance whether it is dealt with as a variable or a constant. Moreover, it has to depend on the relative importance of other explanations.