Aggregated journal-journal citations can be used for mapping the intellectual organization of the sciences in terms of specialties and interreading communities. In addition to indicating local change, probabilistic entropy measures enable us to analyze changes in distributions at different levels of aggregation. The Journal Citation Reports of the Social Science Citation Index for 1999 are compared with similar data for 1998. The indicators are elaborated in relation to similar developments in the Science Citation Index. Specialty formation seems a more important mechanism in the development of the social sciences than in the natural and life sciences, but the developments are volatile. The use of aggregate statistics based on the Science Citation Index is ill-advised in the case of the social sciences because of differences in the underlying dynamics.