Lyo NZY Ribonuclease Inhibitor (no DTT) is a freeze-dried enzyme preparation provided with an optimized reconstitution buffer designed to confer maximal levels of stability and enzymatic activity. The enzyme is subjected to rigorous purification protocols and displays improved resistance to oxidation, which allows it to be stable at DTT concentrations lower than 1 mM. This property makes this ribonuclease inhibitor ideal for reactions that do not tolerate higher levels of DTT (>1 mM) and were RNases (EC 3.1) contamination is a potential problem, such as in real-time RT-PCR assays. Lyo NZY Ribonuclease Inhibitor (no DTT) inhibits the activity of the omnipresent RNases of the pancreatic type, such as RNase A, RNase B and RNase C, by binding them noncovalently in a 1:1 ratio. This enzyme is not active against RNase 1, RNase T1, RNase T2, S1 nuclease and RNase H. Lyo NZY Ribonuclease Inhibitor (no DTT) may be applied in the following applications: cDNA synthesis, RT-PCR, in vitrotranscription, in vitro replication, RNA labelling or RNA isolation and purification.