It is argued that social interaction involves the reciprocal typification of parties to any encounter in the light of the social theories which those parties have available to them. One element of such theories is a conception of the social structure of one's society, including a taxonomy of occupations. Two problems are generated within this taxonomy, that of inclusion, defining what properly falls within some category, and that of exclusion, defining what properly falls out with that category. One way in which these problems are resolved is in the telling of "atrocity stories" which assert and defend the rational character of an occupation and its members against illegitimate claims to its work or to social superiority. These arguments are examined in the light of data derived from a participant-observation study of health visitors, a type of British public health nurse occupying an interstitial role between health and welfare services. The uncertainities of their situation and the role of atrocity stories are examined through a consideration of their relationships with doctors, social workers, other nurses, and ancillary health workers.