The aim of presented studies was to determine which of the two alternative models of working memory (Baddeley's multiple-system model vs Cowan's single-system model) explains performance in various types of memory search task better. In two experiments the authors deal with the peculiar issue of working memory structure and possible role of activation mechanism in searching working memory contents. Both of them applied modified Sternberg's task in which after memorizing a sequence of elements participants had to judge whether the probe element was, or was not, present in the sequence. In Experiment I participants had to memorize stimuli in either one (verbal or visual) or multiple (verbal and visual) modality. In Experiment II subliminal visual priming was used to manipulate the activation of working memory content.The results of Experiment I suggest single-system coding of stimuli in working memory, whereas Experiment II results support the notion of activation as a working memory search mechanism.