We are very good at searching for a visual object in a complex scene when we know its colour, because we can quickly guide our eyes and our attention to locations in the scene that have that colour. When we search for either of two different targets, however, we do not always search efficiently, and thus took longer to find the target. In a series of experiments, we found that subjects searching for two different colours often fixated colours that were very different from either target. This dual-target cost in search performance increases is the similarity between the two target colours increases (split-target cost). There is a similar decrease in search efficiency if subjects hold one colour in visual working memory while searching for another colour (working-memory cost). These costs might reflect fundamental limitations in our abilities to store multiple targets in memory or to use them to guide search. However, in a somewhat different search task with similar stimuli, subjects searched efficiently for two different colours, with relatively few fixations to colours that were dissimilar to both targets. Apparently the attentional system is capable of efficient dual-target search, but subjects sometimes do not employ this capability if there is an alternative way to perform the task, even though this alternative results in a much slower and less efficient search. We hope that these results will lead to ways to improve visual search performance.