Alnico 2. But they are fairly bright pickups for an alnico 2 pickup. I removed mine from my Les Paul Historic and put some Tom Holmes a2 humbuckers in it instead. Much nicer: fuller, warmer and still pretty bright and lively. The 57 Classics are still real nice pickups though...I believe Derek Trucks uses them in his SG and regardless of what some tone snobs might say, the 57 Classics can sound excellant. I prefer Duncan Antiquitys or A2 Gibson Burstbuckers or Fralins or Tom Holmes though. Lew