A large amount of research literature has recently become available on the Internet through "digital libraries". This migration of information from paper to electronic media promises to have a huge impact on the way that research is performed, as documents become more widely, cheaply, and quickly distributed than is possible through traditional publishing. A secondary use for these document repositories and indexes is as a platform for bibliometric research. We examine the extent to which the new digital libraries support conventional bibliometric analysis, and discuss shortcomings in their current forms. Interestingly, these electronic text archives also provide opportunities for new types of studies: generally the full text of documents are available for analysis, giving a finer grain of insight than abstract-only online databases; these repositories often contain technical reports or pre-prints, the "gray literature" that has been previously unavailable for analysis; and document "usage" can be measured directly by recording user accesses, rather than studied indirectly through document references.