Proteins encoded in regions EIA and EIB of human adenoviruses cause transformation of rodent cells. One protein from EIA also stimulates transcription of other early regions at early times in a productive infection. In the past, direct analysis of these proteins synthesized in vivo has been difficult because of the low levels produced in both transformed cells and productively infected cells. We present a simple method which leads to expression of EIA and EIB mRNAs and proteins at 30-fold greater levels than those observed during the early phase of a standard productive infection. Under these conditions, these proteins are among the most prominent translation products of infected cells. This allowed direct visualization of EIA and EIB proteins on two-dimensional gels of pulse-labeled total cell protein. Experiments with EIA and EIB mutants confirm that the identified proteins are indeed encoded in these regions. Two EIA proteins are observed, one translated from each of the major early EIA mRNAs. Both of these EIA proteins are phosphorylated.