Robert Green and Scott Parker were among those joining in training for the first time this summer at a rain-sodden Chadwell Heath on Thursday.
The England duo, who finished last season late after international commitments, were put through their paces alongside Marek Stech, Winston Reid, James Tomkins and Jack Collison, who also had national-team duty beyond the end of May.
Pablo Barrera has been given extra time off because of his exploits at the CONCACAF Gold Cup and will not join his team-mates in Switzerland when they travel this weekend. Gary O'Neil was also back in for the next phase of his rehab, having discarded his crutches following ankle surgery at the end of last season.
The Hammers will take on BSC Young Boys on Monday, although it remains to be seen whether those just returning to action will be involved in that opening fixture of the summer.
The week-long training camp will culminate in a match next Wednesday against FC Basel. Sam Allardyce will also take along some of the club's most promising youngsters and they could get a chance to impress in one or both of the fixtures.
Also involved in training on Thursday was Brazil-born triallist Hernani da Rosa. Hernani, who has Polish citizenship, has spent the last eight years in the Ekstraklasa, most recently with Korona Kielce.
Full picture gallery to follow on whufc.com