For those looking to find strong Medical stocks, it is prudent to search for companies in the group that are outperforming their peers. Is Repligen (RGEN) one of those stocks right now? By taking a look at the stock's year-to-date performance in comparison to its Medical peers, we might be able to answer that question.Repligen is a member of the Medical sector. This group includes 870 individual stocks and currently holds a Zacks Sector Rank of #2. The Zacks Sector Rank considers 16 different groups, measuring the average Zacks Rank of the individual stocks within the sector to gauge the strength of each group.The Zacks Rank is a successful stock-picking model that emphasizes earnings estimates and estimate revisions. The system highlights a number of different stocks that could be poised to outperform the broader market over the next one to three months. RGEN is currently sporting a Zacks Rank of #1 (Strong Buy).Within the past quarter, the Zacks Consensus Estimate for RGEN's full-year earnings has moved 13.98% higher. This signals that analyst sentiment is improving and the stock's earnings outlook is more positive.According to our latest data, RGEN has moved about 66.46% on a year-to-date basis. Meanwhile, the Medical sector has returned an average of 5.34% on a year-to-date basis. As we can see, Repligen is performing better than its sector in the calendar year.Looking more specifically, RGEN belongs to the Medical - Biomedical and Genetics industry, which includes 368 individual stocks and currently sits at #58 in the Zacks Industry Rank. On average, this group has gained an average of 1.71% so far this year, meaning that RGEN is performing better in terms of year-to-date returns.Investors in the Medical sector will want to keep a close eye on RGEN as it attempts to continue its solid performance.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Repligen Corporation (RGEN): Free Stock Analysis Report To read this article on Zacks.com click here.