The level of albumin mRNA and the transcription rate of the albumin gene were studied in the liver of control rats and rats with nephrosis induced by injection of the aminonucleoside of puromycin. Total RNA was extracted from liver by the guanidium thiocyanate method. The albumin mRNA level was measured by cDNA-RNA dot-blot hybridization, and the transcription rate of the albumin gene was measured by the "run-on" transcription assay using isolated nuclei. Urinary protein excretion in nephrotic rats was significantly higher than in control rats (258 +/- 132 vs. 12 +/- 2 mg/day), and the serum albumin concentration in nephrotic rats was significantly lower. There was no difference in body weight, liver weight, serum creatinine, or urea nitrogen between the two groups. Both the level of albumin mRNA and the transcription rate of the albumin gene in the nephrotic liver were about twice as high as those in the control liver. There was no difference in the level of beta-actin mRNA between the two groups. Northern blot analysis showed that both putative precursor RNA and the mature form of albumin mRNA were increased in nephrotic rats. We conclude that albumin synthesis is increased in the liver of nephrotic rats and a transcriptional process is responsible for this increase.