Change in Ratings

American Tower ( AMT - Get Report) downgraded at RBC to sector perform rating from outperform on valuation. Price target and 2008 EBITDA estimates hold at $50 and $1.082 billion, respectively.

Bristol-Myers ( BMY - Get Report) downgraded at Cowen to neutral. Earnings upside may be limited by the generic threat to Plavix.

Crown Castle ( CCI - Get Report) downgraded at RBC to sector perform rating from outperform on valuation. Price target and 2008 EBITDA estimates hold at $47 and $873.9 million, respectively.

Helmerich & Payne ( HP - Get Report) coverage initiated at Goldman Sachs with a buy rating, based on expectations for a major increase in drilling activity over the next six to 18 months. See sustainable competitive advantage and high fleet quality. Price target at $73.

Morgan Stanley ( MS - Get Report) upgraded at Wachovia to outperform. The revision is based upon a higher value of their retail brokerage, good positioning in the prime brokerage business, reduced leverage with the capital infusion and a continuing strength in commodities.

Nabors ( NBR - Get Report) upgraded at Goldman Sachs to buy from neutral based on expected increase in drilling activity. Note attractive valuation, fleet quality and diversification. Price target raised to $48 from $40.

Patterson ( PTEN - Get Report) coverage initiated at Goldman Sachs with a neutral rating. Note recent outperformance in shares and see potential gains from increased drilling activity as already priced in. Price target at $35.

SBA Communications ( SBAC - Get Report) downgraded at RBC to sector perform rating from outperform on valuation. Price target and 2008 EBITDA estimates hold at $41 and $264.1 million, respectively.

Trimble Navigation ( TRMB) downgraded at JPMorgan from overweight to neutral. Stock is up 73% from its January lows, and the risk/reward appears neutral at current levels.

Tyson Foods ( TSN) upgraded at Wachovia to outperform. The week dollar's effect on exports, growing U.S. population and recent closing of a competitor facility are conspiring to restore beef margins toward historical levels.

XenoPort ( XNPT) coverage initiated at Goldman Sachs with a buy rating. See XP13512 as a possible blockbuster with positive phase III results, and potential to launch in 2009. Also note proprietary platform to improve drugs at low risk. Price target at $60.

Stock Comments/EPS Changes

Och-Ziff ( OZM) estimates lowered at Morgan. The 2008 estimate of distributable EPS was lowered to $1.49 from $2.22 with a revised estimate of 7.5% net returns in '08.

Philip Morris ( PM) price target increased at Morgan to $60. Company should see stronger international growth over the coming quarters. Maintain overweight rating.

Sherwin-Williams ( SHW) numbers lowered at UBS. 2008 EPS estimates lowered to $4.00 from $4.75. Price target lowered to $70 from $75. Maintains buy rating.

This article was written by a staff member of TheStreet.com Ratings.