Purpose: This study examined the independent and combined effects of two sources of linguistic knowledge (alphabet cues and semantic predictability) on the intelligibility of speakers with dysarthria. The study also examined the extent to which each source of knowledge accounted for variability in intelligibility gains. Method: Eight speakers with cerebral palsy and dysarthria contributed speech samples, and 128 listeners transcribed the speech samples (16 listeners per speaker) in 4 different conditions (no cues and unpredictable sentences; no cues and predictable sentences; alphabet cues and unpredictable sentences; alphabet cues and predictable sentences). Listener transcription results were the dependent variable and were scored as the percentage of words identified correctly by listeners. Results: Both alphabet cues and semantic predictability made independent and overlapping contributions to intelligibility. In addition, alphabet cues accounted for more of the variability in gain scores than semantic predictability. Inseparable joint effects from the two sources of knowledge also made an important contribution to intelligibility. Conclusion: Alphabet cues may be a more powerful source of information for resolving lexical ambiguity than semantic predictability for listeners who are faced with dysarthric speech. Examples of semantically anomalous sentences and predictable sentences are appended. (Contains 3 tables and 3 figures.)