Eighteen cDNAs, cloned from interferon-treated T98G neuroblastoma cells, correspond to seven different mRNAs induced up to 49fold by interferon. One codes for metallothionein II and another for a class I HLA. The others do not code for proteins of known sequence. In the continued presence of interferon, accumulation of the mRNAs continues for about 1 day but ceases whenever interferon is removed. Once induced, the mRNAs are stable. Synthesis of new proteins is not required for induction. The rate of transcription of one of the genes doubles 5 min after treatment with interferon and reaches a maximum by 80 min. This rate begins to fall after 4-8 hr, reaching the uninduced level by 8-12 hr. Since the mRNA continues to accumulate after 8-12 hr, posttranscriptional events must also play a role in increasing its level.