Transfer across domains has been generally difficult to find. Recent studies have indicated that abstract skills m a y transfer if adequate task analyses are used to define the target skill and people receive the proper training in attaining the skill. This study examined transfer of diagnostic skill across domains for experienced subjects (extensive programming experience but no electronics) aiid inexperienced subjects (no [H-ogramming or electronics experience) when domain-specific information was provided. Four levels of diagnostic skill were identified. Inexperienced subjects could solve problems but did not display an advanced level of diagnostic skill in either domain. However, all experienced subjects displayed high levels of skill on most problems, both in the domain of expertise and in the domain in which they were inexperienced. Results suggest that a general diagnostic skill can transfer spontaneously across domains with extensive practice in one domain and is not acquired to an advanced level without training.