Speculators in IMM yen futures extended a net long position to its largest on record in the week ended January 13, data from the Commodity Futures Trading Commission showed on Friday.
The data from the CFTC's Commitments of Traders report on speculative positioning are used by analysts as an indicator of future market direction.
For example, extreme net long speculative positions often signal a decline in the currency, especially if that position conflicts with the positioning of the more influential commercial players.
Speculators generally comprise trend followers seeking to pick a precise top or bottom in the market.
Yen futures speculators extended the net long position to 60,602 contracts from 56,834 contracts a week earlier.
The dollar was trading near three-year lows against the yen. It has been bolstered periodically by yen-selling intervention by Japanese monetary authorities who think yen strength is a hindrance to economic recovery.
"Intervention is not a fear of spec accounts. You could almost make the case that intervention is being used by these types of traders to add to their position," said Andrew Delano, currency analyst at IDEAglobal in New York. "But there's a pretty good bullish implication for dollar/yen."
Nevertheless, the yen speculative community seems more than willing to perpetuate this yen uptrend as long as the market will tolerate it, Delano said.