In the last trading session, U.S. stocks dipped on weak profit data from China. As for the top ETFs, investors saw (SPY – ETF report) lose 2.5%, (DIA – ETF report) shed 1.9%, while (QQQ – ETF report) moved lower by 2.8% on the day.

Two more specialized ETFs are worth noting in particular as both saw trading volume far outside of normal. In fact, both these funds experienced volume levels that were more than double their average for the most recent trading session. This could make these ETFs the ones to watch in the days ahead to see if this trend of extra-interest continues:

(IBB – ETF report): Volume 5.6 times average

This biotechnology ETF was in focus yesterday as around 11.8 million shares moved hands on the day compared to an average of roughly 2.1 million shares. We also saw some share price movement as shares of IBB fell 6.3% yesterday.

This was the worst trading day performance of the ETF in more than four years. The plunge was driven by a huge sell-off in biotech stocks that we find in this ETF portfolio as Democratic lawmakers severely criticized huge price increases of two heart drugs by Canada's Valeant Pharmaceuticals International, Inc. (VRX – Analyst Report). For the past one month, IBB went down 15%. The fund currently has a Zacks ETF Rank #2 (Buy) with a High risk outlook.

(ITB – ETF report): Volume 3.1 times average

This home construction ETF was in the spotlight as roughly 11.3 million shares moved hands yesterday compared to an average of roughly 3.7 million shares. ITB dropped 4.4% in the session.

The move can largely be blamed on data indicating a more-than-expected decline in pending home sales in August affecting the homebuilding stocks that we find in this ETF portfolio. ITB slid 5.7% in the past one month and it currently has a Zacks ETF Rank #2 with a High risk outlook.