Page 37 Exhibit 11 NATIONAL SERVICE INDUSTRIES, INC. COMPUTATIONS OF NET INCOME PER SHARE OF COMMON STOCK (In thousands, except per-share data) THREE MONTHS ENDED FEBRUARY 28 1998 1997 Basic: Net Income $23,488 $20,345 Basic Weighted Average Number of Shares Outstanding (determined on a monthly basis), including Shares Contingently Issuable 42,765 44,994 $.55 $.45 Diluted: Net Income $23,488 $20,345 Basic Weighted Average Number of Shares Outstanding 42,765 44,994 Add: Shares of common stock assumed issued upon exercise of stock options using the "Treasury Stock" method as it applies to the computation of diluted earnings per share 553 302 Average Common Shares Outstanding (as adjusted) 43,318 45,296 Diluted Earnings per Share $.54 $.45 Page 37 Exhibit 11 NATIONAL SERVICE INDUSTRIES, INC. COMPUTATIONS OF NET INCOME PER SHARE OF COMMON STOCK (In thousands, except per-share data) SIX MONTHS ENDED FEBRUARY 28 1998 1997 Basic: Net Income $50,156 $45,179 Basic Weighted Average Number of Shares Outstanding (determined on a monthly basis), including Shares Contingently Issuable 43,260 45,468 $1.16 $.99 Diluted: Net Income $50,156 $45,179 Basic Weighted Average Number of Shares Outstanding 43,260 45,468 Add: Shares of common stock assumed issued upon exercise of stock options using the "Treasury Stock" method as it applies to the computation of diluted earnings per share 492 281 Average Common Shares Outstanding (as adjusted) 43,752 45,749 Diluted Earnings per Share $1.15 $.99