Former chief minister Buddhadeb Bhattacharjee, who is being treated at Woodlands Hospital, "maintained" blood oxygen saturation levels on Tuesday and his condition was stable, doctors said.
In a bulletin issued on Tuesday evening, the hospital said Bhattacharjee, who was taken off invasive ventilation on Monday, was "maintaining oxygen saturation on non-invasive ventilatory support".
"His overall clinical status remains haemodynamically stable," the statement said.
A doctor said hemodynamically stable means the blood pressure and heart rates of Bhattacharjee, 79, are stable.
A doctor at the hospital said Bhattacharjee spoke to some of his doctors on Tuesday.
The former chief minister was on non-invasive ventilation when he was admitted to the hospital on Saturday afternoon. He was put on invasive ventilation owing to poor "work of breathing" on Sunday. Following improvement in breathing, he was taken off invasive ventilation on Monday.
"He is doing well, but the oxygen and carbon dioxide levels have to be maintained for the next few days. The infection level, which has started to reduce, has to go down further," said a doctor.
CPM leader Rabin Deb and actress Rituparna Sengupta were among those who visited the hospital on Tuesday.
The former chief minister was admitted to the hospital on Saturday afternoon after his blood oxygen level dropped. He was admitted with a "lower respiratory tract infection and Type II respiratory failure", which means his respiratory system was failing to remove carbon dioxide from the body adequately.
A multi-disciplinary medical team has been set up to monitor Bhattacharjee's health.