Frigo's transition to professional cycling began at the 1995
Giro del Veneto, riding as a
stagiaire for . In 1996, he was officially signed to
Saeco on a four-year contract. In 1999, he obtained his first victory at the
Dekra Open, in Germany. In 2000, he joined the
Fassa Bortolo team and achieved success, winning the
Giro di Campania, as well as a stage of the
Giro del Trentino. He also finished second overall in the
Tour de Suisse. More success came for him in early 2001, when he won the time trial at the Col d'Èze and the overall classification of
Paris–Nice, as well as the general classification of the
Tour de Romandie. He entered the
2001 Giro d'Italia and was one of the favorites to win. In the prologue, he finished second to
Rik Verbrugghe and after the fourth stage, he took the race lead, which he held for nine days, until losing it to
Gilberto Simoni on the 13th stage. The gap between the two was very small. On 3 June, Frigo won the 15th stage, a time trial. However, Simoni managed to maintain his lead. On 7 June, the stage was canceled following searches of the NAS in the hotels in Sanremo, where the teams participating in the Giro typically stayed. During the searches of Frigo's vials, doping substances belonging to him were found, but he claimed to have never used them. The next morning, Dario did not leave
Busto Arsizio because he was fired by his team. Later, it was discovered that Frigo had also been scammed because the vial labels did not match the contents of the products. However, Frigo had tried to procure an illicit product, and so he was sentenced to a 6-month ban until 8 March 2002. In 2002, he was hired by
Tacconi Sport and on his return to racing, in
Paris–Nice, he won the hardest stage at the
Col d'Èze. He then won a stage and the final classification of the
Tour de Romandie. He returned to the
Giro d'Italia, but while still managing to stay with the leaders, he finished with a modest 10th place in the standings, 11'50" off the winner
Paolo Savoldelli. After the Giro, he won the national time trial championship and started the
Tour de France, where he won the 17th stage in Megève. After finishing the Tour, he won
Subida a Urkiola and the World Cup Classic
Zurich Metzgete, in August, placing 5th in the
UCI World Ranking. In 2003 he started strong and in the first half of the season he won 6 races: a stage at Paris–Nice, a stage and the final classification both at the
Volta a la Comunitat Valenciana and at the
Setmana Catalana and a stage in the Giro that placed him in 7th overall. Towards the end of the season, he competed in the
Vuelta a España, finishing in twenty-first place. He also took part in the World Championships in both the individual time trial and road race in Hamilton. He ended the season with a third place in the
Giro di Lombardia and finished 14th in the UCI ranking. 2004 was a poor year for Frigo: he was unable to race for three months due to physical problems, and facing a slow and difficult recovery, won no races. In spite of everything, for the second consecutive year he was selected for the
World Championships in
Verona. In 2005, Frigo had another bad season: as he only won one stage in the
Tour de Luxembourg and in July during the
Tour de France, he and his wife were stopped by the French police after ten doses of
EPO were found. After being excluded from the Tour de France, he announced his decision to end his career. == Doping investigation ==