Unilateral nephrectomy in the rat results in contralateral compensatory renal growth. The immediate molecular events which occur in the remaining renal unit were studied by examining RNA isolated from these kidneys. Northern blot analysis was used to analyze the expression of the growth-related (c- fos and c- myc) genes during the 1-hour period following unilateral nephrectomy. Both c- fos and c- myc band transcripts were detected within 15 min after nephrectomy. The immediate, transient induction of these genes in the remaining renal unit mimics that seen during proliferative stimulation of cultured cells and may play a role in modulating the eventual compensatory growth response.