A B757 made an emergency descent as the aircraft's cabin pressurization system lost the ability to properly maintain pressure. Descending through 16;000 FT pressurization stabilized and the crew returned to their departure airport.

Narrative

In cruise at FL370 we heard a slight 'pop' and our ears started popping. Checked the Cabin Altitude Indicator and the cabin rate was pegged. Donned the oxygen masks and called for the checklist while requesting an immediate descent for a pressurization problem from Center. Cabin continued to climb as we descended until we got the Cabin Altitude EICAS message followed shortly after that by the Red Master Warning light and the horn at which time I increased the rate of descent. Descending through the lower twenty's we began to regain control of the cabin and we leveled at 16;000 FT heading toward a nearby airport. We were unable to contact Dispatch for our diversion airport operations so the Controller called for us to tell Dispatch that I was planning on dropping into a diversion airport for fuel and maintenance. Finally raised operations and was informed that other than Mechanics there was no one on duty to handle the aircraft or fuel us. Meanwhile the Center Controller called us to ask if we wanted to terminate the emergency and to tell us that Dispatch was suggesting that we return to our departure airport. Since I was not comfortable with taking the plane back up to a higher altitudes without maintenance checking her first; suspecting that there would be no support available should I have to drop into other enroute airports and concerned that with 18;000 of fuel I could not make my destination at a lower altitude; I chose to return to the departure for an uneventful landing. Maintenance checked the #1 controller and found no faults. Excellent support from the Center Controller; also Company Dispatcher who was on the jump seat with us and night shift maintenance Manager who had all the right folks waiting at the gate to get the jet looked at and take care of the passengers.