This study investigated the impact of the omission of scholarly communication journals from Social Sciences Citation Index (SSCI) and Arts and Humanities Citation Index (AHCI) on citation-based appraisals of communication literature. Citation data were collected from reference lists in articles appearing in 27 communication journals published during 1990, including 14 not indexed by SSCI or AHCI. The 14 journals not included in SSCI or AHCI contributed 1,953, or 26%, of the 7,640 citations to authors during 1990, and 1,156, or 25%, of the 4,587 citations to journals in 1990. Twenty-seven of the 50 most frequently cited authors received 25% or more of their citations from journals omitted by SSCI and AHCI. This study found that an accurate evaluation of a scholar's articles based on citations received will not be possible until SSCI and/or AHCI choose to include the omitted journals, and that computer applications could be used to provide a convenient and inexpensive on-line citation index for communication literature. The Journal Impact Rating, a measure for use in comparing journals’impact on the basis of citations received, was introduced.