FIXED ASSETS

Fixed assets, summarized by major category, consist of the following (in thousands):



	June 30,			December 31,
	2018			2017
Machinery and laboratory equipment	$	41,809		$	39,002
Leasehold improvements	34,932			34,933
Computer equipment and software	7,448			7,086
Office furniture and equipment	1,420			1,603
Construction in progress	79,670			73,632
Total	165,279			156,256
Less: accumulated depreciation	(54,003		)	(49,210		)
Fixed assets, net	$	111,276		$	107,046

For the three months ended June 30, 2018 and 2017, depreciation expense was $2.8 million and $3.7 million, respectively. For each of the three and six month periods ended June 30, 2018 and 2017, capitalized interest on the construction of manufacturing sites was $0.2 million.

For the six months ended June 30, 2018 and 2017, depreciation expense was $5.6 million and $6.8 million, respectively. For the six months ended June 30, 2018 and 2017, capitalized interest on the construction of manufacturing sites was $0.6 million and $0.4 million, respectively.

At June 30, 2018 and December 31, 2017, total fixed assets, net, includes leasehold improvements and manufacturing process equipment located in England in the amount of $65.2 million and $59.8 million, respectively.