Halozyme Therapeutics (HALO) had the highest return in Q4 2006 by a mid-cap US stock, returning 203.8%.

ASSET	QUARTER	% RETURN
Halozyme Therapeutics (HALO)	Q4 2006	203.77%
Energy Fuels (UUUU)	Q4 2006	122.03%
Uranium Energy (UEC)	Q4 2006	105.36%
CorVel (CRVL)	Q4 2006	104.52%
Denison Mines (DNN)	Q4 2006	96.3%
Amkor Technology (AMKR)	Q4 2006	78.93%
Riot Blockchain (RIOT)	Q4 2006	73.53%
Argan (AGX)	Q4 2006	70.79%
First Majestic Silver (AG)	Q4 2006	66.93%
Armstrong World Industries (AWI)	Q4 2006	63.04%
Icahn Enterprises (IEP)	Q4 2006	60.77%
ANI Pharmaceuticals (ANIP)	Q4 2006	57.39%
Dolby Laboratories (DLB)	Q4 2006	57.06%
Formula Systems 1985 Ltd ADR (FORTY)	Q4 2006	51.78%
Millicom International Cellular (TIGO)	Q4 2006	49.98%
Tutor Perini (TPC)	Q4 2006	48.55%
Hudbay Minerals (HBM)	Q4 2006	48.44%
Greif Bros (GEF)	Q4 2006	48.18%
Greif (GEF.B)	Q4 2006	47.91%
Acadia Healthcare (ACHC)	Q4 2006	47.91%
Seaboard (SEB)	Q4 2006	46.54%
Banco Macro SA B ADR (BMA)	Q4 2006	46.18%
Telecom Argentina SA ADR (TEO)	Q4 2006	46.06%
Goodyear Tire & Rubber (GT)	Q4 2006	45.46%
Transportadora de Gas del Sur SA ADR (TGS)	Q4 2006	45.27%

Mid-cap stocks are treated as having a market cap between $2B and $10B.