We present a systematic study of the circular polarization in pulsar i
ntegrated profiles, based on published polarization data. For core com
ponents, we find no significant correlation between the sense change o
f circular polarization and the sense of linear position-angle variati
on. Circular polarization is not restricted to core components and, in
some cases, reversals of circular polarization sense are observed acr
oss the conal emission. In conal double profiles, the sense of circula
r polarization is found to be correlated with the sense of position-an
gle variation. Pulsars with a high degree of linear polarization often
have one hand of circular polarization across the whole profile. For
most pulsars, the sign of circular polarization is the same at 50-cm a
nd 20-cm wavelengths, and the degree of polarization is similar, albei
t with a wide scatter. However, at least two cases of frequency-depend
ent sign reversals are known. This diverse behaviour may require more
than one mechanism to generate circular polarization.