Ranbaxy shares had surged 24 percent in the three trading sessions leading up to the announcement on Monday that Sun Pharmaceutical had agreed to buy it for $3.2 billion.
"We have received multiple complaints. We will ask stock exchanges on details of buy and sell trades in both Ranbaxy and Sun shares," said the source at SEBI.
He declined to be identified because he was not allowed to talk to media about the requests.
Exchange officials at National Stock Exchange of India Ltd and BSE Ltd were not immediately reachable.