A principal component solution and varimax rotation were obtained for eight studies using a serial position (SP) probe technique for studying short-term memory. The factor pattern which emerged showed the first and middle SPs to load on one factor, called the primacy factor, while the middle and last positions loaded on a second factor, called the recency factor. The results were consistent with the view that short-term memory is composed of two processes, primary memory and secondary memory. One study supported the notion that immature humans show a rehearsal deficit.