Radio revenues were mostly flat for the month of May, according to the latest Radio Advertising Bureau Report released yesterday. Local ad sales for the month were flat compared to May of last year, while national dollars rose 4% over the same month a year ago. The combined total for May was also flat when compared to May of 2002. On a year-to-date basis, the industry showed more positive growth, boosted by pre-war ad spending earlier in the year. Local sales figures for the first five months of 2003 were up 1% over the same time period from 2002. National dollars climbed 5% January through May. The combined total for the first five months of 2003 was up 2%, compared to the same five months from last year. The RAB sales index for the month of May was 132.9 for local; 138.7 for national; and 133.5 for the combined total. Looking at the index from a year-to-date perspective, the local index was 134.8; national was 139.2; and the combined total was 135.9.