The 24-year-old Briton, who won in Monaco last year but has struggled with an under-performing McLaren [ Images ] in the first five races of 2009, was third fastest in the morning session and second in the afternoon.
Hamilton's time of one minute 15.445 seconds in the afternoon was the day's second fastest, beaten only by Williams's Nico Rosberg [ Images ] in 1:15.243, and McLaren were constantly among the leaders.
The 23-year-old German Rosberg, son of former champion Keke, has now been quickest in nine of the 17 practice sessions so far this year while failing to translate that promise into anything higher than sixth place on race day.
Brazilian Rubens Barrichello [ Images ], still chasing his first win since 2004, put his championship-leading Brawn GP team mate Jenson Button [ Images ] in the shade with the fastest time of 1:17.189 in the morning and third-best lap after lunch.
Barrichello, who celebrates his 37th birthday in the Mediterranean principality Saturday, lags behind Button by 14 points in the standings.
Button, who is chasing his fifth win in six starts, was eighth on the timesheets in the first practice and fourth in the second.
FERRARI [ Images ] REVIVAL
Although Thursday times mean little, particularly in Monaco with cars jostling for space in tight confines, Barrichello will be boosted after the disappointment of losing out to Button in the previous Spanish Grand Prix that was his for the taking.
Struggling champions Ferrari also enjoyed a revival in their fortunes with Brazilian Felipe Massa [ Images ], who has been on the podium in Monaco for the past two years but has only scored three points so far this season, in the top five in both sessions.
Toyota [ Images ] made a slow start. Italian driver Jarno Trulli [ Images ], a winner in Monaco with Renault [ Images ] in 2004, occupied last position on the timesheets with German team mate Timo Glock [ Images ] 19th in the morning.
BMW-Sauber also failed to impress, with Robert Kubica [ Images ] 16th before lunch and then suffering a fiery engine failure as he accelerated up the hill from Sainte Devote in the afternoon that shrouded the track in smoke.
Red Bull's German Sebastian Vettel [ Images ], the only driver other than Button to win a race this year, suffered an engine failure in the opening practice.