Souza, a 2010 South Atlantic League All-Star shortstop drafted in 2007, and Higley, an outfielder who was Washington's 2008 ninth-round pick, each received 50-game suspensions after testing positive for Methylphenidate and Ritalinic Acid, performance-enhancing substances in violation of the Minor League Drug Prevention and Treatment Program.
The suspensions of Higley and Souza, who are currently on the roster of the club's Class A Hagerstown Suns, are effective immediately.
Methylphenidate is used to treat symptoms of attention deficit hyperactivity disorder and narcolepsy. The medication believed side affects include sudden death, heart attack or stroke in adults with heart conditions.
Souza, selected out of Cascade High School (Everett, Wash.) in '07, has hit below .240 in each of his four professional seasons. He was batting .231 with 11 homers, 56 RBIs and 18 stolen bases in 81 games for Hagerstown this season. He's spent parts of the past three seasons at Hagerstown after spending time with Gulf Coast League Nats and short-season Vermont.
Higley was drafted out of Sacramento Community College and hit .346 in 35 as a rookie in the GCL in '08. He split his second year between Vermont and Hagerstown, batting .276 with five longballs and 26 RBIs. He was hitting .233 with a pair of home runs in 35 games this year.
The Office of the Commissioner of Baseball also suspended a pair of free-agent Minor Leaguers, outfielder Josh Flores and shortstop Manuel Marquez.
Flores, Houston's fourth-round pick in 2005, was banned 50 games after a second positive test for a drug of abuse, while Marquez was suspended 50 games after testing positive for metabolites of Nandrolone, a performance-enhancing substance previously linked to Roger Clemens and Barry Bonds, among others.
Flores was hitting .220 with a homer and two RBIs in 35 games for Class A Advanced Lancaster when he was released by the Astros on June 7. He was a two-time All-Star in '05 and '07 and reached Double-A in 2009 after missing all of 2008.
Marquez was batting .104 in 15 games for the Cardinals' Venezuelan Summer League club until his release June 26.
The suspensions of Flores and Marquez are effective upon their signing with a Major League organization.