EXHIBIT 16.1 [LETTERHEAD OF DELOITTE & TOUCHE LLP] September 25, 1998 Securities and Exchange Commission Mail Stop 9-5 450 5th Street, N.W. Washington, D.C. 20549 Dear Sirs/Madams: We have read and agree with the comments in Item 4 of Form 8-K of Helisys, Inc. dated September 23, 1998. Yours truly, /s/ Deloitte & Touche LLP Deloitte & Touche LLP