ADULT and aged mice were submitted to a discrimination task in a radial maze (regular trials), and then to probe trials requiring them to form relational representations. Three weeks later, animals were again tested for regular and probe trials. Following another interval of 3 weeks, individual hippocampal cytosolic calcium-dependent and -independent PKC activities were measured. Performance of aged animals was impaired on probe but not regular trials and aged mice had lower hippocampal cytosolic calcium-dependent and -independent PKC activities than adults. Performance on probe trials was specifically correlated with calcium-dependent PKC activity. This suggests a specific relationship between the ability to form relational representations and hippocampal cytosolic calcium-dependent PKC activity.