This paper analyzes the communication between science and technology journals (STS), to illustrate patterns of differentiation and integration within scientific fields. First the STS field is delineated, using journal-journal citations as the empirical base. A strong and increasing differentiation is found, between 'qualitative STS', 'quantitative STS' (scientometrics), and 'S&T policy studies'. Given this process of differentiation, the relations between the three sub-fields of STS are analyzed, in terms of mutual flows of information, the joint information base, and research topics. Is differentiation and codification of sub-fields visible? The findings suggest that the relations between qualitative and quantitative STS are one-sided, and that integration between the sub-fields is almost completely lacking. However, the relations between scientometrics and S&T policy studies are much stronger and more substantial, and the same is the case for scientometrics and information science.