Chris Tremlett got a Wasim Akram-less Hampshire off to the best possible start at the Rose Bowl - but then limped off with a foot injury.
Tremlett removed both Somerset openers in his first five overs, either side of Alan Mullally's dismissal of captain Michael Burns, who had won the toss.
He bowled the in-form Peter Bowler with his first ball - the Somerset veteran played on - and then trapped Matthew Wood, who was making his first championship appearance of the season, lbw. That left Somerset reeling on 30-3 in the tenth over, as Mullally had got Burns to edge to Will Kendall at second slip.
No more wickets fell before the rain extended lunch, when Somerset were 72-3, but in the evening session Tremlett hobbled off after receiving treatment from Pat Farhart, and was due to have an X-ray last night.
It is a worry for Tremlett, who suffered a stress fracture of the same foot at the end of last season. But at 6ft 7in he will always be more prone to injury than others.
And Wasim laid low with tonsillitis and Ed Giddins still out with a rib injury, Hampshire's winter arrivals, signed to boost the bowling resources, have been made redundant.
With James Bruce still making the trek from Taunton to the Rose Bowl, he took the field at 1pm, Shaun Udal was brought on earlier than would usually be expected.
The off-spinner's first over was the 13th of the day but it was Mullally and Dimitri Mascarenhas who bowled the bulk of Hampshire's overs.
Udal and left-arm spinner Simon Katich took one wicket apiece; Udal dived low to his left to catch left-hander Ian Blackwell in the last over before tea, while Katich clipped Rob Turner's off stump.
But the wicket of Australian Jamie Cox proved elusive.
After coming in at 18-2, Cox began to show the sort of form that earned him a century and a double ton against Hampshire at Northlands Road in 1999.
His second first-class hundred of the season rescued Somerset, who were a perilous 82-4 when James Bryant was brilliantly run out by James Bruce.
An unbroken stand of 82 for the seventh wicket with Keith Dutch took Somerset into a good position at the end of a day in which a total of 21 overs were lost to rain and bad light.
Cox's unbeaten 101 came from 236 balls and included eight fours on a slow wicket that varied in bounce on occasions - an edge wide of the slip cordon bringing up his 46th first class hundred.
Cox's century against Derbyshire three weeks ago was his first in first class cricket for 45 innings following a barren season for Tasmania, but he was looking ominous last night.
With the help of Dutch, he took Somerset to 224-6 before bad light ended play.
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