This study examines the relationship between various basic mental processing abilities in infancy. Two groups of 7-month-olds received the same delayed-response task to assess visuo-spatial working memory, but two different habituation–dishabituation tasks to assess processing speed and recognition memory. The single-stimulus group (N = 32) was familiarized with only one abstract stimulus, whereas the categorization group (N = 32) received varying exemplars of the same kind. In the categorization group, infants high on working memory showed stronger habituation and dishabituation responses than infants scoring low in working memory. No corresponding relations were found for the single-stimulus group. This suggests that working memory performance is systematically linked to other basic mental skills in 7-month-olds, but that corresponding relations may not get evident in any kind of habituation–dishabituation procedure. Implications for understanding the complex interplay of basic mental abilities in infancy will be discussed.