CNA1 and CNA2 encode isoforms of the catalytic subunit of calcineurin, a Ser/Thr-specific phosphoprotein phosphatase regulated by Ca(2+)/calmodulin. The relative abundance of both transcripts was evaluated during growth of Saccharomyces cerevisiae in glucose by reverse-transcription polymerase chain reaction using PDA1 mRNA as a novel internal standard. CNA1 and CNA2 were concomitantly transcribed with different average expression ratios at the exponential and stationary growth phases and both showed a remarkable drop in the expression at diauxie. Prolonged hyper-osmotic shock resulted in a moderate induction of CNA1, whereas CNA2 expression was not affected.