43, which has an annual turnover of £1m, will be integrated into DLG Digital.
Jeremy Whitaker, DLG's chief executive, said: "The vast network of partners and affiliates which 43 has built up over the years allows DLG instant access to significantly greater audiences of consumers for our ongoing data collection programme.
"The expertise which 43 brings to our digital division also gives us a giant step change in our interactive offering to clients, particularly in terms of web-content, data delivery and revenue generation."
The acquisition of 43 follows DLG's management buy-out in March 2006 and its purchase of Wegener DM UK in 2006. In May this year, the firm was appointed as a data partner to Friends Reunited and has recently launched a mobile offering.
Ian Lowe, 43's managing director, said: "Online data is at the heart of addressable media as convergent technology gathers pace. The combination of DLG's data expertise with 43's digital know-how will put us at the cutting edge of digital marketing."
DLG said it has doubled its profits over the last 12 months and is forecasting 2007/08 sales of £27m and earnings before interest, tax, depreciation and amortisation of £7.9m.
43 was formed in March 2000 to provide a range of interactive online services, including web content, advertising, data collection and bulk email delivery.