The present study investigated comprehension, immediate and delayed vocabulary retention under incidental and intentional learning conditions via computer mediated hypertext gloss. One hundred and eighty four (N = 184) intermediate students of English as a foreign language at an English school participated in the study. They were randomly assigned to either the incidental or the intentional conditions, and received differential treatments. The participants read the same enhanced electronic text with permanently highlighted target vocabularies in the intentional condition, and temporarily highlighted target ones in the incidental condition. The target items were hyperlinked to the same textual enhancements. The results presented the strong and the weak points of the two learning conditions with regards to immediate and delayed retention; as the intentional modality enhanced immediate gain and the incidental one facilitated retention. Consequently, it is recommended that both methods of vocabulary learning can be implemented jointly in a virtual Learning environment in order to improve comprehension and vocabulary retention.