CSL Ltd (ASX: CSL) shares are up 0.3% at $261.87 today, shaking off the broader market sell-down. 

This sees the company with a market cap of almost $127 billion, making it the third largest stock on the ASX.

Over the past year, however, shares in the S&P/ASX 200 Index (ASX: XJO) biotech stock have trailed the benchmark, sliding 9%, while the ASX 200 has gained 8%.

Though those losses were somewhat moderated by the $4.25 a share in unfranked dividends CSL paid out (or shortly will pay out) over the year.

But with CSL shares continuing to struggle in 2025, is the biotech stock one to buy, sell, or hold onto?

Below, we look at the investment case for each option (courtesy of The Bull).

Time to sell CSL shares?

If you ask three different analysts what their outlook is for CSL shares, you may well get three different replies.

With that in mind, Daylight Financial Group's Elio D'Amato has a rather bearish outlook on the stock.

"The biotechnology giant disappointed the market with its first half result in fiscal year 2025," said D'Amato, who has a sell recommendation on CSL stock.

D'Amato noted:

Revenue at the company's vaccine division Seqirus was down 9% due to low immunisation rates, particularly in the US. The plasma collection division CSL Behring remains the key profit driver.

The company is expected to meet full year net profit after tax and amortisation of $3.2 billion to $3.3 billion at constant currency.

Addressing the dawdling share price, D'Amato concluded:

With limited near-term catalysts amid concerns about the outlook for Seqirus, some investors may see better opportunities elsewhere, particularly as the share price has done nothing for years.

Know when to hold 'em

Medallion Financial Group's Stuart Bromley has a more optimistic take on CSL shares.

"The share price of this global healthcare powerhouse was recently punished after posting what investors considered was an underwhelming interim result in fiscal year 2025," said Bromley, who has a hold recommendation on the stock.

Noting that he's "encouraged by CSL's longer-term prospects", Bromley added:

The plasma business Behring performed well and is positioned for growth after rolling out 220 new collection centres. The vaccines business in the first half was weak, but we expect a stronger second half as Northern Hemisphere revenues flow to the business.

The bullish case for CSL shares

Family Financial Solutions' Jabin Hallihan believes the retrace in CSL shares makes the ASX 200 biotech stock attractive at current levels.

"The company's share price recently hit a 52-week low, making it an attractive entry point, in our view," said Hallihan, who has a buy recommendation on the stock.

According to Hallihan:

Despite mixed half year results in fiscal year 2025, the company lifted net profit after tax by 7% at constant currency. A strong performance from CSL Behring amid a dividend increase in Australian currency of 16% on the prior corresponding period highlight its potential.

The company is positioned to deliver annualised double-digit earnings growth in the medium term.