UNLIKE such ill-starred peers as Countrywide Credit or Ameriquest, Thornburg Mortgage was supposed to have been a different kind of home loan company: one that didn’t make so-called Ninja loans (no income, no job, no assets) or engage in any of the other risky practices that led to the subprime debt debacle.

And Thornburg, the nation’s second-largest independent mortgage company, after Countrywide, was indeed more prudent when it came to making loans to prospective home buyers. Mortgage-backed securities issued by Thornburg in 2006 show that only about one-half of 1 percent of the borrowers are delinquent with their payments, compared with a delinquency rate of 6.9 percent in Countrywide’s $1.5 trillion mortgage servicing portfolio.

Indeed, the chief executive of Thornburg, Larry A. Goldstone, has been openly critical of the practices of Countrywide and its leader, Angelo R. Mozilo. During an interview last August with my colleague Floyd Norris and me, Mr. Goldstone pointed out that his company wasn’t even in the subprime business.

True enough, but it hardly matters now. That’s because Thornburg holds billions in mortgage-backed securities that have gone from being regarded as safe to just short of radioactive in recent weeks, causing longtime lenders to demand more collateral from Thornburg. Scrambling to raise cash to pay these margin calls, Thornburg found itself facing bankruptcy rumors last week when its shares dipped below $1. It closed at $2.28 on Friday.