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It’s always a sure bet that when the earnings start to slow to a trickle, the insider activity picks up as windows for top executives and 10% owners open up and they are once again free to trade stock. With the markets once again bumping up against and trading around all-time highs, we were somewhat surprised to see as much insider buying as we did last week.

We cover insider buying each week at 24/7 Wall St., and we like to remind readers that while insider buying is usually a very positive sign, it is not in and of itself a reason to run out and buy a stock. Sometimes insiders and 10% owners have stock purchase plans set up to add to their holdings at intervals. That aside, it still remains an overall positive indicator.

Here are some of the companies that reported notable insider buying last week.

Apollo Global Management LLC (NYSE: APO) had a huge hedge fund again buying shares this past week. Tiger Global Management bought 295,900 shares of the private equity giant at prices that ranged from $26.36 to $26.90. The total for the purchase was reported at 8 million. Earlier in the week, the company bought 1,144,200 shares at prices between $26.47 and $27.18. This trade cost a huge $31 million. The stock closed last Friday at $26.45. The 52-week trading range for the shares is $14.25 to $27.78, and the Wall Street consensus price target is $29.38.

Biogen Inc. (NASDAQ: BIIB) has traded sideways for almost a year, and a director at the biotechnology giant took advantage of the move last week. That board member bought a massive 73,858 shares at prices that ranged from $278.48 to $278.58 apiece. The total for the buy came in at a huge $21 million. But the stock closed on Friday at $262.15. The 52-week range is $223.02 to $333.65. The consensus price objective is $313.94.

Twitter Inc.’s (NYSE: TWTR) long-suffering shareholders will be glad to hear that the co-founder and CEO, Jack Dorsey, was again buying shares of the company last week. The 574,002 shares purchased at prices that ranged from $16.47 to $16.74 cost him some $10 million. Shares closed well above the purchase price on Friday, at $18.69. The 52-week range is $13.73 to $25.25. The consensus price objective is only $14.62.

DDR Corp. (NYSE: DDR) shareholders are also happy to know that a director at this real estate investment trust, which has been hit hard recently, bought a large position last week. The board member bought a 500,000-share block of the stock at prices that ranged from $10.80 to $11.07. The total for the purchase was set at $5 million. The shares closed within striking range of the 52-week low $9.60 last Friday, settling at $9.89. The 52-week high is $19.92.

Radius Health Inc. (NASDAQ: RDUS) had a 10% owner of the biopharmaceutical company adding to its holdings. Biotech Growth bought a 150,000-share block of the stock at $35.39. The total for the trade was set at $5 million. The shares ended the week at $35.75, in a 52-week range of $29.27 to $59.88. The consensus price target is $57.50.

These companies also reported insider buying last week: Bank of America Corp, (NYSE: BAC), Cliffs Natural Resources Inc. (NYSE: CLF), Cree Inc. (NASDAQ: CREE), Superior Energy Services Inc. (NYSE: SPN) and United Continental Holdings Inc. (NYSE: UAL).

As we had reported last month, getting into May would almost assuredly show a spike in insider activity, and that’s just what happened last week. The encouraging thing for investors is the size and volume in the buying which is a positive sign at market highs.