The present study examines the cognitive processes that operate in free recall of categorized lists by manipulating semantic structure of the lists and using a dual task methodology to restrict the processes that make demands on limited-capacity resources, the central executive resources. Relying on the assumption that, in free recall of categorized lists, the search for category names is a strategic controlled process that demands executive resources, lists with different numbers of categories ranging from 2 to 6 were employed. The results showed an effect of a secondary task on retrieval in the 4- and the 6-category list conditions, but not in the 2-category list condition. In contrast to retrieval, the secondary task interference at encoding produced an effect on recall of all three types of lists. An interesting finding was that an effect on clustering was found only when interference was present at encoding, not when it was at retrieval. This finding was in line with the suggestion (Troyer, Moscovitch, Winocur, Alexander, & Stuss, 1998) that switching (shifting between different category items) rather than clustering is related to executive functioning, and suggested that clustering may be a measure of two different types of processing: (1) executive processing at encoding and (2) automatic processing at retrieval. In addition, a different pattern of results was obtained when low frequency category words were used, indicating that the frequency of category words is an important determinant in free recall of categorized lists. Overall, the present results support the two-process account of retrieval of category words (Rosen & Engle, 1997) and the view that there are fundamental differences between encoding and retrieval processes (Naveh-Benjamin, Craik, Guez, Dori, 1998; Naveh-Benjamin & Guez, 2000). (C) 2003 Elsevier Science (USA). All rights reserved.