Best and worst stocks on the ASX at midday

With US markets closed on Monday for the Presidents' Day holiday the local bourse has lacked direction from Wall Street today. At midday the S&P/ASX 200 Index (Index: ^AXJO) (ASX: XJO) was just 0.18% higher. Heavyweights BHP Billiton Limited (ASX: BHP) and Rio Tinto Limited (ASX: RIO) led the gains after BHP released results that beat analysts' expectations.

Here are the top five best performing stocks in the index at midday today:

• Monadelphous Group Limited (ASX: MND)  is up 7.8% to $16.81
• Sirtex Medical Limited (ASX: SRX) has climbed 6.5% to $15.34
• Challenger Ltd  (ASX: CGF) has risen 5.6% to $6.76
• NRW Holdings Limited (ASX: NWH) has added 3.6% to $1.43
• Domino's Pizza Enterprises Ltd. (ASX: DMP) has gained 2.7% to $20.53

These are the five worst performing stocks at midday today:

• Pacific Brands Limited (ASX: PBG) has sunk 11.8% to 63.5 cents
• GWA Group Ltd (ASX: GWA) has lost 6.2% to $2.955
• Coca-Cola Amatil Ltd (ASX: CCL) has dropped 5.8% to $11.16
• Amcor Limited (ASX: AMC) has declined 5.9% to $10.145
• Sirius Resources N.L. (ASX: SIR) is down 5% to $2.49