In September 1994, two network TV series set in fictional Chicago hospitals debuted in the same Thursday night time slot.

One was called "Chicago Hope." The other was called "ER."

I had to decide which one to watch, and I chose "ER," based on the reviews of critics who said the show was gritty and realistic.

These days, it's become routine to see TV characters spurting blood or spewing vomit, and it's easy to forget how revolutionary "ER" was. Previous medical shows had been sanitized melodramas featuring paternalistic doctors like Marcus Welby. "E.R." was the first series that dared to show the ugly reality of medicine.

The show depicts an emergency department that is chronically underfunded and understaffed, overwhelmed by indigent patients who come to the ER for minor problems because they can't afford a primary care doctor.

The ER staff members are caring but overworked and sleep-deprived. They're highly skilled at what they do, but they're human and they make mistakes - occasionally fatal ones. They have to spend a lot of time dealing with gunshot wounds, drug addiction, homelessness and other woes that plague any large urban area.

Throughout the 15-year run of "ER," many characters have come and gone, but that sense of family has always remained. I've never felt that I was watching actors; they seem like real people to me.

That's why it's going to be so hard to say goodbye. On Thursday, "ER" will sign off with a two-hour episode that ties together threads of the show's history, bringing back some of the original characters.

Thursday nights will never be the same. Believe it or not, I have never missed an episode of "ER." If I couldn't be home, I taped it. Sometimes I watched just out of loyalty or habit, during the years when the quality of the writing was disappointing.

Yet even when the storylines left something to be desired, I loved "ER" for its medical accuracy. The characters used the same jargon that real hospital workers do, and they never tried to dumb it down. If you didn't understand what they were talking about, tough. Look up the word; maybe you'll learn something.

At times, though, "ER" wanted to be as clear as possible. Over the years, the show managed to perform a considerable amount of public service by educating viewers about medical issues.

For example, in 2005 there was an episode featuring Cynthia Nixon as a young mother who suffered a stroke. The story was shot from her point of view. She could hear and see what was going on around her, but she couldn't move or speak. She didn't understand what had happened to her or how serious her condition was.

And then, suddenly, she could communicate again. "Clot-busting" drugs, administered within an hour of her stroke, were able to reverse the symptoms. Until that episode aired, many viewers were probably unaware that a stroke can sometimes be "cured" if treated quickly.

Sometimes, "ER" is so accurate it's painful. For me, the turning point of the series came in Season 8, when Dr. Mark Greene, who had always been the heart and soul of the show, succumbed to an aggressive brain tumor known as glioblastoma multiforme.

At the same time that this was unfolding in the fictional world, a close friend of mine was dying of the same type of tumor. My friend was about the same age as Dr. Greene, and like the character, he had a young daughter and a foreign-born wife. The progression of his disease and the course of his treatment were similar to Greene's.

Needless to say, the episodes depicting Greene's deterioration and death were extremely difficult for me to watch. But somehow they also brought a sense of comfort and closure.

I will miss my weekly "ER" visit, just as I miss my friend. But the show has enriched my life in ways that go beyond mere entertainment, and I will always be grateful for the lessons it taught me.